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   2221篇
  免费   173篇
  国内免费   1篇
  2395篇
  2021年   26篇
  2020年   12篇
  2019年   17篇
  2018年   30篇
  2017年   18篇
  2016年   32篇
  2015年   70篇
  2014年   60篇
  2013年   106篇
  2012年   119篇
  2011年   101篇
  2010年   88篇
  2009年   85篇
  2008年   138篇
  2007年   132篇
  2006年   97篇
  2005年   100篇
  2004年   107篇
  2003年   91篇
  2002年   94篇
  2001年   29篇
  2000年   23篇
  1999年   30篇
  1998年   37篇
  1997年   23篇
  1996年   24篇
  1995年   20篇
  1994年   16篇
  1993年   28篇
  1992年   17篇
  1991年   14篇
  1990年   28篇
  1989年   17篇
  1988年   13篇
  1987年   20篇
  1985年   24篇
  1984年   20篇
  1983年   13篇
  1982年   22篇
  1981年   24篇
  1980年   17篇
  1979年   11篇
  1978年   14篇
  1977年   18篇
  1976年   10篇
  1975年   15篇
  1973年   11篇
  1970年   12篇
  1967年   11篇
  1956年   11篇
排序方式: 共有2395条查询结果,搜索用时 15 毫秒
1.
2.
3.
N. Erwin  J. Erwin 《Theriogenology》1976,5(6):261-266
A four-month survey of perineal tumescence in 131 young female pigtail monkeys (Macaca nemestrina) revealed that most females had begun to swell by the time they were 3 years old. Those that had not begun to swell by that time were generally of lower weight than their peers. Those that tumesced before they were 3 years old tended to be heavier than their peers, but were not necessarily heavier than older, nonswelling females.  相似文献   
4.
Indole-3-ethanol (IEt) was extracted from Phycomyces blakesleeanus Bgff. and purified by TLC and HPLC. Identification was performed by mass spectrum. The HPLC-purified compound showed an UV-spectrum typical for indoles, with absorption maxima at 220 and 281 nm. The IEt content varied between 1.5 nmol (g fresh weight)−1 and 5.6 nmol (g fresh weight)−1. The observed variations were strongly correlated with certain developmental stages of the fungus. Furthermore, the decrease of IEt between 60 and 84 h of fungal development coincides with a high IEt oxidase activity. The product of the enzyme reaction was indole-3-acetaldehyde, which was identified by co-chromatography with an authentic standard in several TLC and HPLC systems and by chemical conversion to indole-3-acetaldoxime.  相似文献   
5.
Oral application of a single dose of a new synthetic proteinase inhibitor Camostate (Foy-305) in male Wistar rats was carried out together with studies of in vitro amino acid incorporation followed by separation of proteins by two-dimensional gel electrophoresis. The aim of this experiment was to analyze changes produced by the inhibitor in total protein and individual enzyme biosynthesis. Administration of 100 mg/kg Foy-305 resulted in significant inhibition of total pancreatic protein synthesis, without changes in fractional rates for individual enzymes. 50 mg/kg Foy-305 induced a 10-fold elevation of cholecystokinin (CCK) levels in serum; this persisted for 3 h and led to a significant increase in the total rate of protein synthesis with peak values at 6 and 9 h (78% and 84% above control levels, respectively), returning to control by 15 h. Changes in fractional rates of synthesis occurred with a latency of 6 h and were restricted to amylase and the anionic form of trypsinogen and chymotrypsinogen. Amylase biosynthesis decreased by about 40% from control levels at 9 h to return to control levels by 15 h. Increased synthesis of trypsinogen and chymotrypsinogen was observed; this was also phasic. The results show similar enzyme-specific regulation as previously described for exogenous CCK stimulation and for the adaptation of the pancreas to diets enriched in protein. They demonstrate the effectiveness of pulsatory endogenous hormone release in the regulation of protein synthesis.  相似文献   
6.
Self-organizing maps: stationary states,metastability and convergence rate   总被引:1,自引:0,他引:1  
We investigate the effect of various types of neighborhood function on the convergence rates and the presence or absence of metastable stationary states of Kohonen's self-organizing feature map algorithm in one dimension. We demonstrate that the time necessary to form a topographic representation of the unit interval [0, 1] may vary over several orders of magnitude depending on the range and also the shape of the neighborhood function, by which the weight changes of the neurons in the neighborhood of the winning neuron are scaled. We will prove that for neighborhood functions which are convex on an interval given by the length of the Kohonen chain there exist no metastable states. For all other neighborhood functions, metastable states are present and may trap the algorithm during the learning process. For the widely-used Gaussian function there exists a threshold for the width above which metastable states cannot exist. Due to the presence or absence of metastable states, convergence time is very sensitive to slight changes in the shape of the neighborhood function. Fastest convergence is achieved using neighborhood functions which are "convex" over a large range around the winner neuron and yet have large differences in value at neighboring neurons.  相似文献   
7.
8.
A thorough validation of the bacterial adherence to hydrocarbons (BATH) test was performed by means of a bioluminescence assay. Ten different gram-negative strains were subjected to the BATH test. For the calculation of the adhesion index, several factors had to be taken into account: ATP leakage, the action of ATP-hydrolyzing enzymes, the change in the extraction efficiency of Nucleotide-Releasing Reagent for Microbial Cells (NRB; Lumac bv) after vortexing and the difference in light production after the addition of NRB. When the adhesion index values obtained by bioluminescence measurement were used as reference, the total plate count technique appeared to be unreliable in estimating the number of bacteria adhering to the hydrocarbon phase. A highly significant correlation was established, however, between those reference values and the adhesion index values obtained by the optical density reading for octane and especially for hexadecane. With xylene, no correlation was found between the optical density reading values and the total plate count or bioluminescence values.  相似文献   
9.
From the data presented in this report, the human LDHC gene locus is assigned to chromosome 11. Three genes determine lactate dehydrogenase (LDH) in man. LDHA and LDHB are expressed in most somatic tissues, while expression of LDHC is confined to the germinal epithelium of the testes. A human LDHC cDNA clone was used as a probe to analyze genomic DNA from rodent/human somatic cell hybrids. The pattern of bands with LDHC hybridization is easily distinguished from the pattern detected by LDHA hybridization, and the LDHC probe is specific for testis mRNA. The structural gene LDHA has been previously assigned to human chromosome 11, while LDHB maps to chromosome 12. Studies of pigeon LDH have shown tight linkage between LDHB and LDHC leading to the expectation that these genes would be syntenic in man. However, the data presented in this paper show conclusively that LDHC is syntenic with LDHA on human chromosome 11. The terminology for LDH genes LDHA, LDHB, and LDHC is equivalent to Ldhl, Ldh2, and Ldh3, respectively.  相似文献   
10.
Brain acyl-coenzyme A hydrolase: distribution, purification and properties   总被引:6,自引:0,他引:6  
Rat brain acyl-CoA hydrolase enzymes which hydrolyse C2, C4, C8 and C16 derivatives were localized primarily in the soluble, 144,000 g, supernatant fluid. With octanoyl-CoA as substrate, long-chain acyl-CoA hydrolase activity was greater in the pons, medulla and midbrain than in the cerebral cortex and caudate nucleus. The long-chain acyl-CoA hydrolase enzyme was purified from bovine brain stems to a specific activity of 4-61 n mol of palmitoyl-CoA hydrolysed per min per mg protein. The Km values for palmitoyl-CoA and octanoyl-CoA were 5 μm and 14 μ/m , respectively. Activity of the enzyme was inhibited by bovine serum albumin and ρ-chloromercuribenzoate. The partially purified enzyme protein was found to have approximately eight titratable sulphydryl residues per 105 g of protein. Studies of the molecular weight of the enzyme indicated the presence of associated and dissociated forms with molecular weights of approximately 96,000 and 46,000 respectively.  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