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   14479篇
  免费   1247篇
  国内免费   5篇
  2023年   43篇
  2022年   94篇
  2021年   228篇
  2020年   113篇
  2019年   184篇
  2018年   195篇
  2017年   174篇
  2016年   382篇
  2015年   581篇
  2014年   757篇
  2013年   865篇
  2012年   1097篇
  2011年   1075篇
  2010年   709篇
  2009年   631篇
  2008年   902篇
  2007年   872篇
  2006年   841篇
  2005年   769篇
  2004年   748篇
  2003年   758篇
  2002年   704篇
  2001年   145篇
  2000年   139篇
  1999年   169篇
  1998年   222篇
  1997年   147篇
  1996年   126篇
  1995年   144篇
  1994年   115篇
  1993年   134篇
  1992年   137篇
  1991年   99篇
  1990年   87篇
  1989年   82篇
  1988年   71篇
  1987年   55篇
  1986年   74篇
  1985年   69篇
  1984年   84篇
  1983年   48篇
  1982年   65篇
  1981年   50篇
  1980年   45篇
  1979年   53篇
  1978年   41篇
  1977年   54篇
  1976年   36篇
  1974年   41篇
  1973年   43篇
排序方式: 共有10000条查询结果,搜索用时 140 毫秒
61.
62.
Oskar is one of seven Drosophila maternal-effect genes that are necessary for germline and abdomen formation. We have cloned oskar and show that oskar RNA is localized to the posterior pole of the oocyte when germ plasm forms. This polar distribution of oskar RNA is established during oogenesis in three phases: accumulation in the oocyte, transport toward the posterior, and finally maintenance at the posterior pole of the oocyte. The colocalization of oskar and nanos in wild-type and bicaudal embryos suggests that oskar directs localization of the posterior determinant nanos. We propose that the pole plasm is assembled stepwise and that continued interaction among its components is required for germ cell determination.  相似文献   
63.
Summary Cuticle/water partition coefficients (Kc/w) for d-limonene, -pinene and -pinene were determined by an extrapolation and a desorption method. The sorption experiments were carried out with isolated angiosperm and gymnosperm cuticles and with [14C]-labelled monoterpenes, which were obtained biosynthetically. Both methods were suitable for the determination of the Kc/w of volatile hydrophobic compounds. For the angiosperm cuticles the partition coefficients are of the order of 104, which indicates a high accumulation of monoterpenes in the cuticle. The values of the conifer cuticles of Picea abies (L.) Karst. and Abies alba Mill., however, are lower due to their high lignin content. This is proved by the increase of the partition coefficients after removal of polar and phenolic components. The Kc/w can be estimated with good accuracy from the octanol/water partition coefficient, which was determined experimentally.  相似文献   
64.
65.
The use of toluidine blue for in situ detection of micro-organisms in foods   总被引:1,自引:0,他引:1  
The use of toluidine blue to stain cryosections of food samples to detect sites of microbial growth was examined. The method successfully detected colonies and single cells of both yeasts and bacteria at magnifications of x 400 or below in the majority of foods studied. The method demonstrates great potential for studying the micro-environments in which micro-organisms grow.  相似文献   
66.
The kinetic behavior andpH-stability of recombinant human renin was analyzed using a new fluorogenic substrate based on the normal P6-P3 renin cleavage sequence in human angiotensinogen. The design of this fluorogenic substrate makes possible, for the first time, direct monitoring of the kinetics of proteolytic conversion of prorenin to renin. ThepH-stability profile for renin, measured with the substrate at 25°C, indicated a broad plateau of stability betweenpH 6.0 and 10.0. Analysis of thepH-activity profile of renin for the substrate indicated a minimumK m (1.8 µM) atpH 7.4 and a maximumV m betweenpH 7.4 and 8.0. The thermodynamics of the binding of a novel, soluble, peptidomimetic inhibitor to renin indicated it is possible to retain the tight-binding characteristics and enthalpy contributions to binding of larger peptide-derived inhibitors, while reducing inhibitor size and entropic contributions to binding. A novel derivative of the fluorogenic substrate, containing a 3-methyl histidine substitution at the P2 site, was used to test the recent hypothesis that renin functions by virtue of substrate-directed catalysis.  相似文献   
67.
68.
Summary Applying a double-immunofluorescence technique, the porcine ovary is demonstrated to receive two populations of NPY-immunoreactive nerve fibres originating from the inferior mesenteric ganglion: one with colocalized tyrosine hydroxylase and supplying predominantly the ovarian vasculature, and a second, solely NPY-immunoreactive and almost exclusively associated with growing follicles. A third group of tyrosine hydroxylase-and dopamine--hydroxylase-positive, but NPY-negative nerve fibres is associated with ovarian blood vessels and, to a minor extent, with ovarian follicles. As revealed by retrograde tracing, the vast majority of postganglionic neurons projecting to the ovary is located in a discrete area of the ganglion, suggesting a somatotopic organization of the porcine inferior mesenteric ganglion. Moreover, the finding indicate that three subpopulations of postganglionic sympathetic neurons with different chemical codes supply different target components of the porcine ovary. The physiological relevance of the described neurons in the nervous control of ovarian functions remains to be elucidated.A portion of these results has been presented in abstract form (Majewski et al. 1991)  相似文献   
69.
Genomic organization of the retinoic acid receptor gamma gene.   总被引:5,自引:1,他引:4       下载免费PDF全文
  相似文献   
70.
Gamma radiation sensitivities of continuous cell lines from nine human tumours were measured, comparing four derived from transitional cell carcinomas of the bladder with five from non-seminomatous germ cell tumours of the testis. The testicular cells were significantly more radiosensitive than the bladder cells, corresponding to the response to therapy of these tumour types in patients. These observations indicate that radiosensitivity is retained in vitro and is an inherent property of the testicular tumour cells. These gamma radiation sensitivities were compared with those of SV40-transformed fibroblasts derived from a normal individual and one with the heritable disease, ataxia-telangiectasia (A-T). The bladder cells had gamma radiation sensitivities similar to that of the SV40-transformed normal line. The testicular cells were hypersensitive to gamma radiation, although not as sensitive as the SV40-transformed A-T line. A-T cells, unlike those derived from normal individuals, continue to synthesize DNA at a normal rate following radiation exposure, prompting a comparison of the kinetics of DNA synthesis in three bladder and three testicular tumour cell lines. One of the bladder and two testicular lines showed a reduced inhibition when compared to the other tumour cell lines and the SV40-transformed normal line. Thus there was no clear association between DNA synthesis inhibition and radiosensitivity.  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