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   15160篇
  免费   1027篇
  国内免费   156篇
耳鼻咽喉   200篇
儿科学   341篇
妇产科学   164篇
基础医学   1874篇
口腔科学   270篇
临床医学   1201篇
内科学   3957篇
皮肤病学   304篇
神经病学   1038篇
特种医学   621篇
外科学   2165篇
综合类   207篇
一般理论   21篇
预防医学   1101篇
眼科学   351篇
药学   921篇
中国医学   60篇
肿瘤学   1547篇
  2023年   93篇
  2022年   162篇
  2021年   349篇
  2020年   237篇
  2019年   334篇
  2018年   374篇
  2017年   355篇
  2016年   397篇
  2015年   440篇
  2014年   558篇
  2013年   689篇
  2012年   1122篇
  2011年   1076篇
  2010年   675篇
  2009年   528篇
  2008年   1005篇
  2007年   1123篇
  2006年   992篇
  2005年   1053篇
  2004年   897篇
  2003年   967篇
  2002年   915篇
  2001年   147篇
  2000年   119篇
  1999年   150篇
  1998年   170篇
  1997年   181篇
  1996年   144篇
  1995年   134篇
  1994年   89篇
  1993年   83篇
  1992年   74篇
  1991年   59篇
  1990年   58篇
  1989年   48篇
  1988年   43篇
  1987年   42篇
  1986年   26篇
  1985年   28篇
  1984年   34篇
  1983年   34篇
  1982年   30篇
  1981年   24篇
  1980年   31篇
  1979年   22篇
  1978年   25篇
  1977年   30篇
  1976年   17篇
  1973年   15篇
  1966年   16篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
91.
IMMUNOHISTOCHEMICAL DISTRIBUTION OF CANNABINOID CB 1 RECEPTOR IN THE RAT CENTRAL NERVOUS SYSTEM@邹冈  相似文献   
92.
Two series of block copolymers have been synthesized comprising of soft polytrifluoroacetaldehyde (polyacetal) segments and of hard 4,4′-methylenedi(phenyl isocyanate)/cis-cyclohexane-1,4-diol polyurethane segments. The series-A copolymers in which the soft segments were directly bound to the hard segments had significantly lower thermal stability than the series-B copolymers in which the soft segments were linked to the hard segments by sebacic ester units. In both series the thermal stability decreased with increasing soft segment content. The series-A copolymers exhibited two thermal transitions both characteristic of Tg's and separated by about 60 K. In contrast the series-B copolymers exhibited two characteristic Tg's separated by 200–250 K, depending on composition, together with an additional endothermic transition at about ambient temperature. All transitions for both series decreased with increasing soft segment content. The observations have been compared with those of other polyether and polyester based polyurethanes.  相似文献   
93.
Four cases of Ischemic enterocolitis without arterio–occlusive lesion were described. Three cases were associated with sigmoid colon carcinomas. Ischemic lesions developed anal to the carcinomas in two cases, and oral to sigmoidostomy to relieve intestinal obstruction by carcinoma in one case. One other case was associated with inguinal hernia. Grossly, ischemic lesions involved relatively short intestinal segments, and the ischemic colonic lesions were not related to teniae coli. Extensive veno–occlusive lesions were discovered in a case of ischemic stricture of the ileum, which had been incarcerated in the right inguinal hernia. Reversible mechanical occlusion of the intestinal vessels caused by transient or recurrent intestinal strangulation is the most probable cause of these ischemic lesions., ACTA PATHOL. JPN. 33: 249–256, 1983.  相似文献   
94.
Pulmonary metastasis from low-grade endometrial stromal sarcomas (ESSs) occasionally are found after long, disease-free periods, mostly as incidental histological or radiological discoveries. We describe a case of low-grade ESS presenting as nodular pulmonary metastases finally diagnosed by estrogen-receptor staining, cytogenetic and fluorescence in situ hybridization (FISH) analyses, and perusal of the histology of hysterectomy material. An abnormal nodule in the lung field was discovered by means of chest X-ray of a 47-year-old woman. She had been disease free for 13 years after hysterectomy for an alleged leiomyoma. A computed tomographic scan revealed nodules, with fluctuation in size over the 2-year period, in both lungs. Finally the lesion in the left lung was resected, and pulmonary endometriosis was suspected because of the lack of stromal cell nuclear atypia and positive immunohistochemical reactions for estrogen and progesterone receptors. However, a characteristic karyotype was identified cytogenetically: 46, XX, t(7;17)(p15;q11), the translocation of which, specific to ESS, was confirmed by FISH analysis. A final diagnosis of pulmonary metastases from an ESS could be made by reviewing the histology of the previous uterine tumor. In this case, metastatic lesions from an ESS showed a decrease as well as an increase in size, despite the malignant potential. Immunostaining for estrogen and progesterone receptors and cytogenetic and FISH analyses, together with clinical information on the past gynecological history, are valuable diagnostic keys.  相似文献   
95.
Thymic nurse cells (TNC), multicellular complexes consisting of lymphoid cells enclosed within cortical epithelial cells, were isolated from mouse thymus by a modified procedure allowing immunofluorescent labeling and flow cytometric analysis of their lymphoid contents (TNC-L). Collagenase was the only protease used for tissue digestion, to ensure that surface antigen markers remained intact. Zonal unit-gravity elutriation was used to enrich the TNC on the basis of their high sedimentation rate, followed by immunomagnetic bead depletion to remove residual mononuclear cell contaminants and a density separation to remove debris. The TNC-L were then released from inside TNC by a short period of culture. The measured contamination of TNC-L with exogenous thymocytes was around 0.5%. Three-color immunofluorescent labeling revealed that TNC-L included, as well as a maiority of immature CD4+8+3low thymocytes, about 12% of apparently mature CD4+8-3high and CD4-8+3high thymocytes. TNC are located in the cortex, where mature cells are rare; the occurrence of mature phenotype cells within these structures suggests that they represent a microenvironment for the selection and generation of mature T cells.  相似文献   
96.
Utilizing real-time computer image analysis, individual spermatozoawere selected using microaspiration. Selection criteria werebased on potential hyperactivation motility characteristics;the amplitude of lateral head displacement >7.5 µm,curvilinear velocity >70 µm/s and linearity of <30%.For this pilot study, 16 patients (eight in each group) wererecruited. Using subzonal insemination (SUZI), up to five (mean= 4.4 ± 0.3) spermatozoa selected using computer-imagesperm selection (CISS) were microinjected, or up to 15 (mean= 12.8 ± 1.3 SD) unselected spermatozoa. In the groupwhich utilized CISS, 28 out of 49 (57%) oocytes were fertilizedcompared with 13 out of 52 (25%) utilizing conventional SUZI(P < 0.04); polyspermy was 20% (n = 10) and 2% (n = 1) respectively.CISS with SUZI showed increased efficiency in achieving fertilizationand is a novel approach to studying individual sperm functionin a sperm egg bioassay where gamete ratios are close to unity.  相似文献   
97.
Oligostyryllithium was synthesized by the reaction of sec-butyllithium with styrene in diethyl ether at ?40°C. Dimer model anions (counter cations: Li and K) of the growing chain ends were synthesized by metallation of 1-methoxy-1,3-diphenylpropane. The structures of the lithium compounds were corroborated by 13C NMR spectroscopy and compared with those of the potassium compounds. As for polystyryllithium and its model compounds, the charge density on the α-carbon increased and that on the phenyl ring of the growing end decreased with increasing molecular weight, while, in polystyrylpotassium and its model compounds, the charge density on the α-carbon increased and the one on the phenyl ring did not change with increasing molecular weight. The temperature change of the 1H NMR spectrum of oligostyryllithium in diethyl ether indicated rotation around the C-1? Cα bond at lower temperatures than in tetrahydrofuran, but the activation energy was the same in both solvents. T1 values of the phenyl carbons in model compound 2b were one to two orders of magnitude shorter than those of the protonated compound.  相似文献   
98.
Modulation by protein phosphorylation of the relation between acetylcholine (ACh)-activated current (I ACh) and adenosine triphosphate-(ATP)-activated current (I ATP) was investigated with the whole-cell voltage-clamp technique in rat sympathetic neurons. During simultaneous activation by 100 M ATP of an inward current, the current evoked by 100 M ACh was reduced to 60–70% of that in the absence of ATP. Effects of compounds that are known to modulate protein phosphorylation were tested by including them in the intracellular solution. The reduction ofI ACh by ATP was not observed when K252a (1 M), a non-selective protein kinase inhibitor, adenosine 5-O-(3-thiotriphosphate) (ATP[S], 1 mM) or,-methylene ATP (1 mM) were included in the intracellular solution. Activators of protein kinases, adenosine 3,5-cyclic monophosphate (cAMP, 100 M), guanosine 3,5-cyclic monophosphate (cGMP, 100 M), phorbol 12-myristate 13-acetate (PMA, 1 M), also abolished the reduction by ATP ofI ACh. The effects of okadaic acid, a protein phosphatase inhibitor, were paradoxical: okadaic acid (2 M) itself abolished the reduction by ATP ofI ACh but it antagonized the abolishment by cAMP or cGMP of the reduction ofI ACh. Okadaic acid did not affect the disappearance of the reduction ofI ACh by ATP in the presence of intracellular PMA. The results suggest that the interaction betweenI ACh andI ATP is regulated by protein phosphorylation/dephosphorylation. Possible mechanisms underlying the effects of these modulators of protein phosphorylation are discussed.  相似文献   
99.
100.
炎症性肠病动物模型的研究概况   总被引:2,自引:0,他引:2       下载免费PDF全文
The etiology and pathogenesis of inflammatory bowel disease are up to now still not clear and definite. Establishing the ideal animal model to study its cause and pathogenesis of this disease is very important. The ideal animal model should have the same manifestation with human inflammatory bowel disease on clinical and pathologic feature etc. In this article, the method, the pathologic character isfics and concerning pathogenesis, of a few common useful experiment animal models are discussed.  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