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   23856篇
  免费   1150篇
  国内免费   159篇
耳鼻咽喉   210篇
儿科学   543篇
妇产科学   280篇
基础医学   3262篇
口腔科学   413篇
临床医学   1424篇
内科学   6345篇
皮肤病学   580篇
神经病学   1760篇
特种医学   979篇
外科学   4006篇
综合类   123篇
预防医学   566篇
眼科学   573篇
药学   1474篇
中国医学   41篇
肿瘤学   2586篇
  2023年   140篇
  2022年   291篇
  2021年   490篇
  2020年   276篇
  2019年   354篇
  2018年   506篇
  2017年   389篇
  2016年   477篇
  2015年   500篇
  2014年   730篇
  2013年   817篇
  2012年   1397篇
  2011年   1577篇
  2010年   880篇
  2009年   795篇
  2008年   1391篇
  2007年   1548篇
  2006年   1513篇
  2005年   1654篇
  2004年   1661篇
  2003年   1698篇
  2002年   1574篇
  2001年   296篇
  2000年   243篇
  1999年   327篇
  1998年   402篇
  1997年   324篇
  1996年   313篇
  1995年   269篇
  1994年   243篇
  1993年   221篇
  1992年   172篇
  1991年   150篇
  1990年   139篇
  1989年   118篇
  1988年   124篇
  1987年   101篇
  1986年   103篇
  1985年   99篇
  1984年   106篇
  1983年   78篇
  1982年   77篇
  1981年   78篇
  1980年   72篇
  1979年   58篇
  1978年   51篇
  1977年   47篇
  1976年   41篇
  1975年   32篇
  1972年   28篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
81.
The acid-catalyzed condensation of formaldehyde and diphenyl sulfide was carried out in benzene in the presence of p-toluene sulfonic acid. From the products, four poly(methylene diphenyl sulfides) of the following structures were isolated.   相似文献   
82.
A case of glioblastoma arising in the pons of a 14-year-old boy in whom transsynaptic degeneration was found in the inferior olivary nucleus is reported. The tumor occupied most of the pons including the tegmental tract and invaded into the midbrain, medulla oblongata, cerebellar peduncles, thalamus, basal ganglia, and meninges. The right inferior olivary nucleus was devoid of the tumorous lesion, but many neurons were severely vacuolated. An im-munohistochemical study using glial fibrillary acidic protein (GFAP), neuron-specific enolase (NSE), and S-100 protein was performed. GFAP and S-100 protein were positive in the reactive glia of the nucleus and NSE gave a faint reaction in some degenerated neurons. These degenerative changes found in neurons of the inferior olivary nucleus were considered to be transsynaptic degeneration due to the destruction of the tegmental tract at the pons and of cerebellar peduncles by invasive pontine glioblastoma. ACTA PATHOL. JPN. 35: 1495–1500, 1985.  相似文献   
83.
Although various genetic factors have been implicated in human male infertility, the causative genes for the different types of idiopathic male infertility have not been elucidated. Protamines, which are the major DNA-binding proteins in the sperm nucleus, package the DNA into the sperm head. Analysis of the human protamine-1 (PRM1) and -2 (PRM2) gene sequences in 226 sterile male patients and in 270 proven-fertile male volunteers revealed four single nucleotide polymorphisms (SNPs) in the PRM1 coding region, which did not cause any amino acid substitutions, and one SNP in the PRM2 gene, which produced translation termination. We also observed one SNP in the 3' non-coding region of the PRM1 gene, and two SNPs within the intron of the PRM2 gene. The prevalence of these SNPs was similar in both infertile patients and in proven-fertile volunteers, except that the c248t alteration in the PRM2 gene induced a nonsense codon under conditions of heterozygosity in one infertile patient. Although the PRM1 and PRM2 genes are highly conserved, the single SNP in the PRM2 gene that induces translation termination may result in male infertility due to haploinsufficiency of PRM2.  相似文献   
84.
Genetic contributions to the etiology of substance abuse and dependence are topics of major interest. Acute and chronic cannabis use can produce drug-induced psychosis resembling schizophrenia and worsen positive symptoms of schizophrenia. The endocannabinoid system is one of the most important neural signaling pathways implicated in substance abuse and dependence. The fatty acid amide hydrolase (FAAH) is a primary catabolic enzyme of endocannabinoids. To clarify a possible involvement of FAAH in the etiology of methamphetamine dependence/psychosis or schizophrenia, we examined the genetic association of a nonsynonymous polymorphism of the FAAH gene (Pro129Thr) by a case-control study. We found no significant association in allele and genotype frequencies of the polymorphism with either disorder. Because the Pro129Thr polymorphism reduces enzyme instability, it is unlikely that dysfunction of FAAH and enhanced endocannabinoid system induce susceptibility to either methamphetamine dependence/psychosis or schizophrenia.  相似文献   
85.
Summary The Ca2+-dependent intercellular adhesion molecule cadherin is known to be linked to the cytoskeleton by the protein catenin, an association of which appears to be important for the cell-adhesion function of cadherin. Catenin consists of three subtypes-, , and . In our previous study, N-cadherin was shown to be localized on the plasmalemma of normal and regenerating chick peripheral nerve. Thus, as N-catenin is a subtype of -catenin (which is specifically associated with N-cadherin), we investigated the immunolocalization of N-catenin in normal and regenerating chick sciatic nerve. In normal nerve, unmyelinated axons exhibited either intense or weak N-catenin immunoreactivity throughout the axoplasm, whereas myelinated axons were completely immunonegative. Regenerating axons, including those derived from parent myelinated axons, showed N-catenin immunoreactivity of variable intensities in growth cones and axon shafts. Schwann cells were invariably devoid of immunoreactivity. Thus N-catenin is not necessarily bound to the surface plasmalemma, but is distributed throughout the cytoplasm, suggesting that most N-catenin molecules are dissociated from N-cadherin.  相似文献   
86.
87.
Background: The presence of efferent fibers in the anteromedial eye of liphistiid spiders kept in natural daily cycles of illuminance has been reported. However, this report is limited to innervation by the efferent fiber and daily rhabdomal changes, and there have been no detailed ultrastructural accounts of the eye. Methods: The fine structure of this eye was examined by electron microscopy. Results and conclusions: The eye consists of a cornea, a lens, a vitreous body, and a retina. The retina contains 13 or 14 receptor cells and glial cells. The rhabdoms are distal to the nuclei of the receptor cells. In the distal region of the receptive segment, the rhabdomeres lie in the center of the cell. In the middle region, anisomorphic rhabdoms formed by microvilli from adjacent cells are at the cell periphery. In the proximal region, the rhabdomeres are situated in the center of the cell. The ocellar nerve of the eye runs toward the protocerebrum and enters the posterior part of the first optic ganglion of the secondary eyes. Pigmented cells and nonpigmented cells are observed. The pigmented cells are located in the most lateral of the eye and cover the whole eye. The nonpigmented cells are located in the receptor cell bodies and extend to the origin of the ocellar nerve. They wind to form capillaries filled with electron-dense material. These structures are discussed in comparison with those of other spiders and other chelicerates. © 1994 Wiley-Liss, Inc.  相似文献   
88.
89.
90.
DIPN induced localized lesions of the rat thyroid gland are described histologically and classified into three major types: type 1, foci of cellular alteration; type 2, proliferative nodules; and type 3, overt carcinomas. Follicular, papillary and mixed papillofollicular subtypes are recognized in the type 2 lesions, and follicular, papillary, anaplastic and mixed subtypes in the type 3 lesions. The nature of the individual lesions is 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