首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   69587篇
  免费   5136篇
  国内免费   2539篇
耳鼻咽喉   466篇
儿科学   1515篇
妇产科学   950篇
基础医学   10658篇
口腔科学   1079篇
临床医学   5262篇
内科学   10478篇
皮肤病学   1401篇
神经病学   5011篇
特种医学   1043篇
外国民族医学   13篇
外科学   5178篇
综合类   8116篇
现状与发展   11篇
预防医学   5562篇
眼科学   1049篇
药学   11022篇
  13篇
中国医学   3320篇
肿瘤学   5115篇
  2023年   980篇
  2022年   1747篇
  2021年   2218篇
  2020年   2090篇
  2019年   2705篇
  2018年   2599篇
  2017年   2253篇
  2016年   2145篇
  2015年   2389篇
  2014年   3728篇
  2013年   4461篇
  2012年   3831篇
  2011年   4664篇
  2010年   3870篇
  2009年   3282篇
  2008年   3149篇
  2007年   3042篇
  2006年   2625篇
  2005年   2253篇
  2004年   2037篇
  2003年   1891篇
  2002年   1579篇
  2001年   1436篇
  2000年   1184篇
  1999年   1124篇
  1998年   859篇
  1997年   778篇
  1996年   639篇
  1995年   554篇
  1994年   495篇
  1993年   441篇
  1992年   416篇
  1991年   368篇
  1990年   333篇
  1989年   271篇
  1988年   263篇
  1987年   197篇
  1985年   836篇
  1984年   1070篇
  1983年   835篇
  1982年   975篇
  1981年   914篇
  1980年   683篇
  1979年   634篇
  1978年   457篇
  1977年   364篇
  1976年   419篇
  1975年   323篇
  1974年   203篇
  1973年   204篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
21.
In search of potential drugs for the treatment of estrogen- and androgen-dependent cancer as well as the prophylaxis of metastases, tetralones, tetralins, and dihydronaphthalenes bearing a OCH3 substituent at the benzene nucleus and an imidazol-4-yl, imidazol-1-yl, or 1,2,4-triazol-1-yl substituent in 2-position were synthesized with and without C1-spacer between the rings (compounds 2 – 26 ). The compounds were tested in vitro for inhibition of the three target enzymes P450 arom (human placental microsomes), P450 17 (rat testicular microsomes), and P450 TxA2 (citrated human whole blood). To examine selectivity, some compounds were further tested in vitro for inhibition of P450 18 (bovine adrenal mitochondria), P450 see (bovine adrenal mitochondria) and corticoid formation (aldosterone, corticosterone; ACTH stimulated rat adrenal tissue). In vivo, selected compounds were examined in Sprague Dawley rats regarding P450 TxA2 inhibition, reduction of plasma testosterone concentration, antiuterotrophic activity (inhibition of the uterotrophic activity of androstenedione), reduction of plasma estradiol concentration (pregnant mares' serum gonadotropin-primed rats), and mammary tumor inhibiting activity (dimethylbenzanthracene-induced tumor; pre- and postmenopausal model). In the series of imidazol-4-yl compounds, which represent a novelty in the field of azole inhibitors of steroidogenic P450 enzymes, strong inhibitors of P450 arom and/or P450 17 were found: 7-OCH3-2-(imidazol-4-ylmethylene)-1-tetralone ( 4 ) and 7-OCH3-2-(imidazol-4-ylmethyl)-tetralin ( 12 ) are among the most potent inhibitors of P450 arom in vitro known so far. Compound 4 is a selective inhibitor, whereas 12 shows in addition strong inhibition of P450 17. In contrast to 12 , the 6-OCH3 derivative (compound 11 ) is a selective inhibitor of P450 17, being 50 times more potent than ketoconazole. Some imidazol-1-yl compounds show a marked inhibition of P450 TxA2: 2-(imidazol-1-ylmethyl)-1-tetralone ( 13 ) is a selective inhibitor of P450 TxA2, whereas 7-OCH3-2-(imidazol-1-ylmethyl)-tetralin ( 17 ) as well as 2-(imidazol-1-ylmethyl)-tetralin ( 16 ) and 7-OCH3-2-imidazol-1-yl-3,4-dihydronaphthalene ( 25 ) additionally show strong inhibition of P450 arom and P450 17. Regarding the other steroidogenic P450 enzymes as well as corticosterone formation, the compounds show only little inhibitory activity. Aldosterone formation, however, is inhibited at low concentrations. Nevertheless, 4 and 12 are more selective, i.e. inhibit aldosterone synthesis less than the well known inhibitor of P450 arom fadrozole. The compounds show activity in the aforementioned in vivo tests.  相似文献   
22.
1. Endothelium-dependent relaxation in response to acetylcholine (ACh) and the calcium ionophore A 23187 was examined in aorta, coronary, basilar and renal arteries isolated from Watanabe heritable hyperlipidaemic (WHHL) rabbits of 2, 6 and 12 months of age, with normolipidaemic heterozygous WHHL rabbits as controls. 2. In the rings of WHHL rabbit aortae and coronary arteries preconstricted with vasoconstrictors, endothelium-dependent relaxation in response to ACh was attenuated with age compared to the heterozygous WHHL rabbits. A significant negative correlation was found between the total cholesterol content and the relaxation response to ACh in the aortae or coronary arteries from 6 and 12 month old WHHL rabbits. 3. In the rings of basilar arteries, endothelium-dependent relaxations to ACh were not modified with age. Similarly, in the rings of renal arteries, the relaxation response to ACh was not changed with age, but in the 6 and 12 month preparations, after the age of 6 months, a contraction following the relaxation appeared at higher concentrations of ACh (10?7 to 10?6 mol/L). The contraction was endothelium-dependent and inhibited by indomethacin. 4. A 23187-induced endothelium-dependent relaxations were also markedly attenuated in the aorta and significantly in the coronary artery with age. 5. Endothelium-independent relaxation to sodium nitroprusside was not changed in all arteries from WHHL rabbits of different ages. 6. These findings indicate that in the aorta and coronary artery of the WHHL rabbit, the endothelium-dependent relaxation to ACh and A 23187 becomes impaired with increasing age (i.e., with the progression of cholesterol deposition in the arterial wall) but is preserved in the basilar and renal artery.  相似文献   
23.
Growth of cultured NlE-115 neuroblastoma cells in 1 μM A23187 for 2 days to elevate internal Ca reduced both membrane Na current and the transient, but not steady state, component of outward K current. Na channel mRNA abundance was reduced by an average value of 45% without effect on Kv3.1. Increases in internal Ca may therefore control excitability by independent regulation of Na and K channel mRNA abundance in neurons.  相似文献   
24.
BACKGROUND: A subgroup of children with obsessive-compulsive and tic disorders are proposed to have an infectious trigger. The purpose of this study was to investigate the relationship between group A streptococcal titers and symptom fluctuations in children with a clinical course resembling that described for pediatric autoimmune neuropsychiatric disorders associated with streptococcus. METHODS: Twenty-five children with obsessive-compulsive disorder and/or tic disorder were evaluated for neuropsychiatric severity and group A streptococcal antibody titers (streptolysin O, deoxyribonuclease B, and carbohydrate A) at 6-week intervals for > or = six consecutive evaluations (total visits=277). RESULTS: Children with large symptom fluctuations (n=15) were compared with children without dramatic fluctuations (n=10). Co-movements of obsessive-compulsive/tic severity and group A streptococcal antibodies were assessed. In subjects with large symptom changes, positive correlations were found between streptococcal titers and obsessive-compulsive severity rating changes (p=.0130). These subjects were also more likely to have elevated group A streptococcal titers during the majority of observations (p=.001). Tic symptom exacerbations occurred more often in the fall/winter months than spring/summer months (p=.03). CONCLUSIONS: Patients with marked obsessive-compulsive/tic symptom changes may be characterized by streptococcal titer elevations and exhibit evidence of seasonal tic exacerbations.  相似文献   
25.
Zusammenfassung Wir berichten fiber die Doppler-sonographischen Ergebnisse bei 33 Patienten mit einer Anastomose zwischen der A. temporalis superficialis and der A. cerebri media. Die Indikation zur Bypass-Operation beinhaltete rezidivierende TIA oder ein kurz zuvor erworbenes leichtes neurologisches Defizit bei angiographischem Nachweis einseitiger oder beidseitiger tiefer Obliterationen der A. carotis interna und hochgradiger Stenosen oder Verschlüsse im distalen Abschnitt der A. carotis interna bzw. im proximalen Abschnitt der A. cerebri media. Die Funktionsfahigkeit der Anastomose wurde überpriift durch die Berechnung der modifizier ten Pourcelot-Indices (relative enddiastolische Strömungsgeschwindigkeit) der A. temporalis superficialis praeauriculär und am Bohrlochrand Bowie durch den EinfluB der intermittierenden Kompression des den Bypass-versorgenden Gefäßes auf den modifizierten Pourcelot-Index der ipsilateralen A. carotis communis. Bei allen Patienten mit funktionsfahigen Anastomosen, definiert durch einen modifizierten Pourcelot-Index von zumindest 0,20 am Bohrlochrand, kam es zu einer Reduktion dieses Parameters um durchschnittlich 0,08 an der A. carotis communis bei kurzfristiger Kompression des den Bypass-versorgenden Astes. Bei den 18 Patienten mit unilateraler Obliteration der A. carotis interna war der Bypass über-wiegend dann funktionsfähig, wenn die summierten modifizierten Pourcelot-Indices der verbliebenen hirnversorgenden Gefäße um zumindest 10% gegenüber einem vergleichbaren Normalkollektiv reduziert waren. Das Vorhandensein bzw. das Fehlen von Ophthalmica-Kollateralen hatte dabei keinen Einfluß auf den Prozentsatz der funktionsfahigen Anastomosen in diesen Untergruppen. Bei den vier Patienten mit bilateraler Obliteration der A. carotis interna war die angelegte Anastomose in jedem Fall funktionsfähig, während die Hälfte der Patienten mit Stenosen and Verschlüssen im distalen Abschnitt der Carotisstrombahn nur eine ungeniigende Bypass-Funktion zeigten. Die zwei Patienten mit einer Mediahauptstammstenose bzw. -obliteration hatten Indices von 0,45 bzw. 0,46 am Bohrlochrand als Hinweis auf die Funktionstüchtigkeit. Wir Bind der Auffassung, daß man mittels Doppler-sonographischer Kriterien die Funktionsfahigkeit einer Temporalis superficialis-Cerebri media-Anastomose überprüfen kann. Der praeoperativ berechnete summierte modifizierte Pourcelot-Index der verbliebenen hirnversorgenden Arterien kann zumindest bei uni- and bilateraler Internaobliteration als zusatzlicher Parameter herangezogen werden, um die Indikation zur Bypass-Operation zu klären.  相似文献   
26.
Zusammenfassung Die Humerusschaftfraktur ist in 10–18% der Fälle durch primäre Radialisparese kompliziert. Sekundäre Radialisläsionen treten iatrogen bei intramedullären Verfahren in 3%, bei Plattenosteosynthesen in 15,5% auf. In der überwiegenden Mehrzahl der Fälle (80%) ist der Radialisschaden rückläufig. Eine Verletzung der A. radialis ist eher selten; sie erfordert ein offenes Vorgehen mit lokaler Revision des Gefäßes und Frakturversorgung mittels Plattenosteosynthese. Die Marknagelosteosynthese ist bei einfachen, komplexen oder pathologischen Schaftfrakturen primär oder als Verfahrenswechsel nach primärer Fixateuranlage indiziert. Während auch ausgewählte Frakturen im Collum chirurgicum mit einem Nagel versorgt werden können, sind Frakturen im distalen Viertel des Humerus ausgeschlossen. Frakturen bei kleinen Kopffragmenten weisen ein erhöhtes Komplikationsrisiko auf. Zur Vermeidung von Läsionen der Rotatorenmanschette stehen wir der anterograden Nagelung noch zurückhaltend gegenüber. Bei differenzierter Indikationsstellung und Nachbehandlung erwies sich die retrograde Marknagelung als ein schonendes Verfahren mit hohem Patientenkomfort und gutem funktionellem Ergebnis.  相似文献   
27.
Serum IgA and IgG functional antibodies and their subclasses to Streptococcus pneumoniae capsular antigen found in two aged‐matched cohorts of children with and without otitis media with effusion The relationship between acute otitis media and otitis media with effusion (OME) is uncertain and the aetiology of OME is multifactorial. Otitis media with effusion may be an inflammatory condition; both bacteria and viral infections could play a part in this inflammation. The four bacteria Streptococcus pneumoniae, Haemophilus influenza, Staphylococcus aureus and Branhamella catarrhalis cause 60% of the infections whereas S. pneumoniae accounts for up to 35%. IgA provides the dominant surface response to polysaccharide and lipopolysaccharide antigens, of which IgA2 is the main subclass. Once the mucosa has been breached, most protection is provided by IgG. IgG2 acts mainly against bacterial capsular antigens. This study looked at two groups of 50 children with and without OME who were aged between 3 and 10 years. The aims were to determine if, firstly, the levels of the serum immunoglobulins were different in the two groups, secondly whether these children made the appropriate antibody response to the capsular antigen to S. pneumoniae (PCP), and finally if there was a delay in the maturity of the IgA response. The total IgG, IgA and all subclass levels were measured using radial immunodiffusion. Levels of functional IgA and IgG were measured using ELISAs (25 patients in each group). The results were analysed with non‐parametric tests. The immunoglobulin levels were within the normal levels for both groups. There were very good correlations between the IgG total anti‐PCP and the IgG2 anti‐PCP (R > 0.9, p = 0.001). There was a good correlation between the levels of both IgG total and IgG2 anti‐PCP against IgA total anti‐PCP in both groups (R > 0.85, p > 0.01). This confirms a normal antibody response between both groups of patients. The ages of the controls and patients (50 samples) were correlated with increasing titres of circulating functional antibodies (P = 0.001). This is highly suggestive of a normal age‐related response. In conclusion, the findings were contradictory to our original hypothesis that there is a subtle difference in surface protection between children with and without OME. We believe that a previous history of recurrent acute otitis media is unrelated to the development of OME after 3 years of age.  相似文献   
28.
Synkinesias secondary to nerve lesions and aberrant re-innervation are well-known phenomena especially after lesions of the facial nerve. Synkinesias can successfully be treated with botulinum toxin A (BTx A). Synkinesias of the cremaster muscle have not been described or treated to date. We present the case of a 62-year-old man who developed synkinesias of both cremaster muscles after extensive laparatomy for esophageal cancer. Treatment of synkinesias with various oral medications had been unsuccessful. Electromyography-guided injections of BTx A in both cremaster muscles (15 MU on the right and 10 on the left) led to significant symptom relief for an average of 8 weeks. We present the case including pre- and posttreatment video clips.  相似文献   
29.
BACKGROUND: The mucosal mast cell (MMC) granule-specific beta-chymase, mouse mast cell protease-1 (mMCP-1), is released systemically into the bloodstream early in nematode infection before parasite-specific IgE responses develop and TGF-beta1 induces constitutive release of mMCP-1 by homologues of MMC in vitro. Intraepithelial MMC may also express the chemokine CCL2 (monocyte chemotactic protein-1) during nematode infection but the expression of this chemokine by MMC homologues has not been investigated. OBJECTIVE: To investigate the expression and to compare the mechanisms of constitutive release of the chymase, mMCP-1, and the chemokine, CCL2. METHODS: MMC homologues were generated by culturing bone marrow cells in the presence of TGF-beta1, IL-3, IL-9 and stem cell factor (SCF). The intracellular distribution of mMCP-1 and CCL2 was examined by confocal microscopy. The involvement of the Golgi complex and of protein synthesis in the constitutive release of mMCP-1 and CCL2 was investigated using the Golgi-disrupting agent brefeldin A and cycloheximide to block protein synthesis. Secreted analytes were quantified by ELISA. RESULTS: mMCP-1 colocalized with Golgi matrix protein 130 but was most abundant in the granules, whereas CCL2 was not found in the granules but appeared to be located uniquely in the Golgi complex. Extracellular release of mMCP-1 was significantly inhibited ( approximately 40%) by cycloheximide and by the Golgi-disrupting agent brefeldin A, indicating both continuous protein synthesis and transportation via the Golgi complex are required for optimal mMCP-1 secretion. A similar but more marked inhibitory effect with both compounds was demonstrated on the constitutive secretion of CCL2. CONCLUSION: The culture conditions that promote mMCP-1 expression and release by MMC homologues also promote the expression and release of CCL2. Constitutive release involves de novo protein synthesis and requires a functional Golgi complex, suggesting that similar mechanisms of extracellular secretion operate for both mediators.  相似文献   
30.
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号