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   3555篇
  免费   322篇
  国内免费   20篇
耳鼻咽喉   27篇
儿科学   95篇
妇产科学   166篇
基础医学   342篇
口腔科学   89篇
临床医学   477篇
内科学   656篇
皮肤病学   46篇
神经病学   353篇
特种医学   149篇
外科学   352篇
综合类   78篇
一般理论   4篇
预防医学   399篇
眼科学   27篇
药学   486篇
中国医学   4篇
肿瘤学   147篇
  2021年   35篇
  2020年   44篇
  2019年   41篇
  2018年   58篇
  2017年   42篇
  2016年   44篇
  2015年   72篇
  2014年   82篇
  2013年   131篇
  2012年   164篇
  2011年   168篇
  2010年   124篇
  2009年   113篇
  2008年   137篇
  2007年   161篇
  2006年   124篇
  2005年   123篇
  2004年   148篇
  2003年   134篇
  2002年   132篇
  2001年   128篇
  2000年   122篇
  1999年   113篇
  1998年   61篇
  1997年   68篇
  1996年   58篇
  1995年   57篇
  1994年   31篇
  1993年   40篇
  1992年   71篇
  1991年   83篇
  1990年   80篇
  1989年   78篇
  1988年   77篇
  1987年   61篇
  1986年   62篇
  1985年   56篇
  1984年   55篇
  1983年   38篇
  1982年   27篇
  1981年   36篇
  1980年   22篇
  1979年   37篇
  1978年   26篇
  1977年   32篇
  1976年   32篇
  1975年   28篇
  1974年   26篇
  1970年   23篇
  1969年   23篇
排序方式: 共有3897条查询结果,搜索用时 12 毫秒
31.
We previously showed that HIV-1 gp120-induced apoptosis in primary human umbilical vein endothelial cell cultures (HUVEC), through CCR5 and CXCR4. Here, we have found that agonists of protein kinase C (PKC), basic fibroblast growth factor (bFGF), and short exposure to low concentrations of phorbol esters were found to block gp120-induced apoptosis in HUVEC cultures. PKC antagonists, sphingosine, H7, and extended exposure of cultures to high concentrations of phorbol esters were also found to block gp120-induced apoptosis in HUVEC cultures. A significant increase in the total amount of cellular PKC enzymatic activity was observed on exposure of HUVEC to gp120. No increase in total PKC activity was observed on exposure of HUVECs to the natural ligands SDF-1alpha, or regulated-on-activation normal T-expressed and secreted (RANTES) cells, and gp120-induced PKC induction was found to be totally blocked by CXCR4 antibodies and partially blocked by the caspase 3 inhibitor, DEVD-CHO. Alternatively, CXCR4 antibodies and DEVD-CHO totally blocked apoptosis. Finally, gp120-induced effects were found to be insensitive to pertussis toxin. Accumulated evidence suggests PKC involvement at multiple points in the gp120-induced apoptotic pathway; also suggests involvement of the CXCR4 receptor internalization pathway, and potentially suggests different downstream effects of gp120-receptor interactions and natural ligand-receptor interactions.  相似文献   
32.
33.
C57BL/6J (B6) and DBA/2J (D2) mice differ in maternal behavior and nest building, but previous observations on nest building appear to be contradictory. Lactating B6 females spent more time nest building than lactating D2 females [Physiol. Behav. 67 (1999) 599.]; however, pregnant D2 females have been reported to build better nests than pregnant B6 females [Physiol. Behav. 29 (1982) 153.]. To resolve this apparent discrepancy, virgin B6 and D2 females were mated, and the nest quality of nulligravid, primigravid and lactating primiparous females was compared between groups and with that of virgin females. There were no strain differences in the nest ratings of virgin or mated nulligravid females, nor did these groups differ within strains. Pregnant and lactating females of both strains built better nests than nonpregnant females. There was an increase in nest ratings in both strains on the day of parturition. The nest ratings of pregnant and lactating females were higher in B6 than D2 females. The largest strain differences were observed between pregnant B6 and D2 females. One hypothesis to account for these results is that females of these two strains differ in their levels of or sensitivity to hormones during pregnancy and parturition.  相似文献   
34.
The effects of the patch test application of Malassezia pachydermatis extracts to normal canine skin were evaluated in eight healthy beagle dogs. Antigens (4 and 0.4 mg/ml) and saline controls were applied for 48 h using filter paper discs in Finn chambers. At the first test, two dogs showed patch test reactivity 20 min and 24 h after patch removal. Four out of six dogs that did not react to the first patch test showed reactivity when re-tested on day 8. Two remaining dogs were patch tested for a third time on day 15, after 7 days of cutaneous challenge with suspensions of M. pachydermatis cells, but failed to display reactivity. Positive patch test reactions were characterized histologically by mild epidermal hyperplasia, superficial dermal oedema and mild to moderate perivascular, periadnexal and interstitial infiltrates of neutrophils and CD3+ lymphocytes. Four dogs showed delayed intradermal test reactivity to M. pachydermatis antigens but intradermal and patch test reactivity did not correlate. This study indicates that patch test reactivity to M. pachydermatis antigen occurs in some healthy dogs exposed to the yeast, or may develop after a short period of antigen exposure. Further studies of patch test reactivity are warranted in dogs with disease associated with this cutaneous yeast.  相似文献   
35.
BACKGROUND: Pathological gambling is more prevalent among postsecondary students than among the general adult population. While the prevalence of pathological gambling in this group has risen over the past decade, factors underlying the development of problem gambling among university students remain largely unexplored. One early study found alexithymia to be associated with pathological gambling. The aim of the present study was to further examine the relationship between alexithymia and gambling among postsecondary students. METHODS: The relationship between alexithymia and pathological gambling was examined in 562 postsecondary students who completed the South Oaks Gambling Screen (SOGS) and the 20-item Toronto Alexithymia Scale (TAS-20). RESULTS: Approximately 12% of the sample was classified as alexithymic according to the TAS-20. These individuals were found to have significantly more gambling problems, as measured by the SOGS, than nonalexithymic individuals. Approximately 9% of the sample was classified as pathological gamblers according to the SOGS. These individuals were found to have significantly higher levels of alexithymia, as measured by the TAS-20, than nonproblem gamblers. CONCLUSIONS: Alexithymia is associated with pathological gambling and may be a risk factor among postsecondary students for developing severe gambling problems.  相似文献   
36.
An infant girl with elevated blood lactate, pyruvate, and plasma branched-chain amino acids was diagnosed with dihydrolipoamide dehydrogenase (E3; dihydrolipoamide: NAD+ oxidoreductase, EC 1.8.1.4) deficiency. Activities of the pyruvate dehydrogenase complex and E3 from patient were 26 and 2% of controls in blood lymphocytes, and 11 and 14% in cultured skin fibroblasts, respectively. Western blot analysis demonstrated that the amount of E3 protein in fibroblasts from the patient and her father was about half of controls, while Northern blot analysis showed normal amounts of E3 RNA. DNA sequencing of cloned full-length E3 cDNAs from the patient revealed two mutations in separate alleles. One is a single base insertion of an extra adenine in the last codon of the leader peptide sequence (TAC-->TAAC) leading to a nonsense mutation which results in the premature termination of the precursor E3 polypeptide (Y35X). The other is a missense mutation due to substitution of guanine for adenine, causing an Arg-->Gly substitution at amino acid 460 of the mature protein (R460G) which triggers the loss of E3 activity probably by structural change in the E3 dimer. DNA sequencing of E3 cDNAs from the parents demonstrated that the nonsense mutation was inherited from the father and the missense mutation was inherited from the mother.   相似文献   
37.
Filamentous myosin is present in both relaxed (myosin light chains unphosphorylated) and contracted (light chains phosphorylated) vascular smooth muscle. The organization of myosin and actin filaments and the insertion of the latter on cytoplasmic and plasma membrane bound dense bodies is consistent with a mini sarcomere-like organization and a sliding filament mechanism of contraction in smooth muscle. Mitochondria are high capacity, low affinity Ca stores in smooth muscle. They do not play a role in the regulation of cytoplasmic Ca2+ at physiological levels. The localization and Ca content of the junctional sarcoplasmatic reticulum (SR) is consistent with this organelle being the major intracellular source of activator Ca released by excitatory transmitters. Repeated contractions in the absence of extracellular Ca2+ (thought to represent recycling of intracellular activator Ca2+) can be demonstrated if the excitatory agent is not allowed to remain in contact with the smooth muscle throughout relaxation; the demonstration of “recycling” is facilitated if the efflux of cellular Ca2+ is blocked. The rise in total cytoplasmic calcium measured with electron probe analysis during a maintained (30 min) contracture in rabbit portal-anterior mesenteric vein smooth muscle (∼0.9 mmol/kg dry cytoplasm) is greater than the amount of Ca that could be bound to calmodulin.  相似文献   
38.
The marital adjustment of patients with psychogenic pain disorder was evaluated and compared with a matched group of patients with other neurotic disorders. Pain patients spouses were found to have better marital adjustment and less psychiatric morbidity than the spouses of neurotic patients. These findings are discussed in terms of the concepts of "sick role homeostasis" and "tertiary gain".  相似文献   
39.
The Journal of Behavioral Health Services & Research - Individuals recently released from jail or prison with serious mental illnesses may be vulnerable to the coronavirus pandemic. This study...  相似文献   
40.
BackgroundOur aim in this study was to identify the fibular footprint of the Anterior Inferior Tibiofibular Ligament (AITFL) and its relation to Wagstaffe fracture fragment size.MethodsWe examined 25 cadaveric lower limbs which were carefully dissected to identify the lateral ankle ligaments. The AITFL anatomy was compared to 40 Wagstaffe fractures identified from our ankle fracture database.ResultsThe AITFL origin was from the anterior fibular tubercle with an average length of 21.61 mm (95% CI 20.22, 22.99). The average distance of the distal aspect of the AITFL footprint to the distal fibula margin was 11.60 mm (95% CI 10.49, 12.71). In the ankle fractures analyzed, the average length of the Wagstaffe fragment was 17.88 mm (95% CI 16.21, 19.54). The average distance from the distal tip of the fibula to the Wagstaffe fracture fragment was 21.40 mm (95% CI 19.78, 23.01).In total there were 22 syndesmosis injuries. There was no statistical difference in Wagstaffe fragment size between stable and unstable groups.ConclusionThe AITFL fibular origin was both larger and more distal than the Wagstaffe fracture fragments seen in our institution. Therefore, this suggests that a ligamentous failure will also have to occur to result in syndesmotic instability. The size of fracture fragment also did not confer to syndesmotic instability on testing.Level of Evidence - 3  相似文献   
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