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   3788篇
  免费   303篇
  国内免费   16篇
  2023年   17篇
  2022年   18篇
  2021年   72篇
  2020年   36篇
  2019年   47篇
  2018年   81篇
  2017年   69篇
  2016年   103篇
  2015年   182篇
  2014年   213篇
  2013年   241篇
  2012年   328篇
  2011年   273篇
  2010年   151篇
  2009年   141篇
  2008年   197篇
  2007年   180篇
  2006年   193篇
  2005年   151篇
  2004年   139篇
  2003年   132篇
  2002年   98篇
  2001年   104篇
  2000年   82篇
  1999年   94篇
  1998年   39篇
  1997年   25篇
  1996年   19篇
  1994年   23篇
  1993年   19篇
  1992年   54篇
  1991年   48篇
  1990年   49篇
  1989年   27篇
  1988年   30篇
  1987年   34篇
  1986年   33篇
  1985年   38篇
  1984年   27篇
  1983年   29篇
  1982年   22篇
  1981年   16篇
  1980年   16篇
  1979年   26篇
  1978年   23篇
  1977年   21篇
  1976年   24篇
  1975年   20篇
  1973年   16篇
  1972年   16篇
排序方式: 共有4107条查询结果,搜索用时 15 毫秒
1.

Purpose  

Though the development of biofuel has attracted numerous studies for quantifying potential water demand applying life cycle thinking, the impacts of biofuel water consumption still remain unknown. In this study, we aimed to quantify ecological impact associated with corn-based bioethanol water consumption in Minnesota in responding to different refinery expansion scenarios by applying a life cycle impact assessment method.  相似文献   
2.
Study of the posterior abdominal epidermis in hypophysectomized/thyroidectomized male and female tokays following surgery, and subsequent androgen therapy, indicates that, contrary to a previous model, all aspects of β-gland differentiation are under direct androgenic control. On the other hand, another epidermal specialization, the digital foot-pad, shows a pattern of histogenesis directly comparable to that of β-glands, but is unaffected by androgens. These data are discussed with respect to the evolution of glandular epidermal specializations in gekkonid lizards and the possible role of androgens in modifying the control of cell differentiation in lizard epidermis.  相似文献   
3.
4.
Looking for an appropriate model of accelerated aging in vivo we investigated the content of endogenous products of lipid peroxidation (LP) in the rat brain after single or 4 day-lasting intramuscular injection of complex-bind iron (ferum Hausman, 50 mg/kg body weight) like promoter of LP. We found that the single administration of this iron complex fails to induce endogenous LP; after 4 day-application of iron we observed significant increase in content of primary (lipid peroxides) and final (fluorescent) products of LP. Iron-promoted activation of endogenous LP could be abolished by animal pretreatment with the natural antioxidant alpha-tocopherol. The calcium antagonist nifedipine didn't affect the content of endogenous LP products neither alone nor in combination with alpha-tocopherol.  相似文献   
5.
The course of acute infection of mice with ts mutant or the native strain DNA and the antigens of HSV in brain nerve cells were determined. Virus DNA was detected in brains of all mice in both animal groups while the virus antigens--only in cells of mice infected with the native strain. It can be suggested, therefore, that the ability of ts mutant to replicate in central nervous system of the infected mice is lacking or much lower. The detection of virus nucleic acid 3-5 months after virus infection might indicate a possibility of establishing latent infection. However, ts mutant showed a significantly lower possibility of latency induction, as compared with highly virulent strains. It was found that the mutant ability to induce latent infection was markedly increased when mice were treated with both ts mutant and Depo-Medrol as immunosuppressive agent. This finding shows both a possibility of increase of frequency of latent infections in the state of immunosuppression, and of activation of the latent infection (recurrence of acute form of infection).  相似文献   
6.
A rapid and sensitive radioimmunoassay has been developed for measurements of atrial natriuretic factor (ANF) in rat plasma. The antiserum, raised to rat ANF (99-126), cross-reacts with rat ANF (103-123), ANF (103-125), ANF (103-126) but not with smaller fragments, human ANF (99-126), angiotensin II, bradykinin or vasopressin. The plasma ANF concentration is 181 +/- 24 pg/ml (N = 24) in the unstressed conscious rats (Charles River CD, male). The ANF immunoreactivity in the plasma extracts was verified by HPLC analysis, which displayed one major immunoreactive peak of ANF corresponding to rat ANF (99-126) and some smaller fragments. Intravenous injection of saline elevated circulating ANF, whereas acute volume depletion by hemorrhage, water deprivation and furosemide diuresis greatly lowered plasma ANF. The prompt response of plasma ANF levels to acute changes in volume status is consistent with the proposed role of ANF as a volume-regulatory hormone.  相似文献   
7.
We have previously reported that the covalent attachment of phosphoinositides to myelin basic protein (MBP) occurs both in vivo and in vitro [Smith, R. A. et al. (1986) Biochemistry 25:2677-2681; Biochemistry 25:2682-2686; and Biochem. Biophys. Res. Comm. 316:426-432]. Phosphoinositidation of MBP was also detected when [32P] phosphoinositides were incubated with myelin pretreated with Triton X-100 and EGTA. Less than 10% of this covalent linkage of phosphoinositides to MBP survived after acidic treatment (0.1 N HCl at 37 degrees C for 10 min). MBP is predicted to lack sufficient hydrophobicity to bind to membranes as shown by analysis of its amino acid sequence for hydrophobic regions and thus its phosphoinositidation may provide an anchor for this purpose.  相似文献   
8.
Salmonella rods of subspecies I, lactose-fermenting were first isolated in Poland in 1980. They were isolated from a plus sample taken from a brain abscess of a child. Next strains were isolated from faeces of newborn and hospitalized children. Growth characteristic of colonies of lactose-fermenting Salmonella strains on selective-differentiating media (Mac Conkey's Levine, SS, So?tys) recommended for inoculation of clinical material resembled Escherichia coli. So far these type of colonies were omitted in diagnostic examinations. Lactose-fermenting variants showed on Bismuth sulfate agar "Difco" (WB) typical for Salmonella growth pattern. They grew on this medium after 48 hr of incubation in a form of black, medium sized colonies, with some metallic brilliance and characteristic blackening of the medium undercolonies. Precise knowledge of biochemical properties of lactose-fermenting Salmonella allows to supplement so far used diagnostic scheme with additional tests permitting differentiation of lactose-fermenting variants of Salmonella from the other members of Enterobacteriaceae family. Taking into consideration biochemical variants in diagnostic procedure i.e. lactose-fermenting Salmonella, allowedns to isolate in the years 1983-1985 lactose-positive strains in 1305 out of 2773 (47%) individuals positive for S. agona. In 1987, 246 persons (28.3%) out of 869 with lactose-fermenting Salmonella of various serotypes were simultaneously infected with lactose-negative variant. Lactose-fermenting strains of Salmonella belonged most frequently to the following genera: S. agona, S. enteritidis, S. oranienburg, S. typhimurium, and S. goldcoast. It was found that the modified diagnostic procedure makes possible the isolation and the identification of lactose-positive varians of Salmonella.  相似文献   
9.
Three-dimensional structure of the HSV1 nucleocapsid   总被引:26,自引:0,他引:26  
J D Schrag  B V Prasad  F J Rixon  W Chiu 《Cell》1989,56(4):651-660
The three-dimensional structures of full and empty capsids of HSV1 were determined by computer analysis of low dose cryo-electron images of ice embedded capsids. The full capsid structure is organized into outer, intermediate, and inner structural layers. The empty capsid structure has only one layer which is indistinguishable from the outer layer of the full capsids. This layer is arranged according to T = 16 icosahedral symmetry. The intermediate layer of full capsids appears to lie on a T = 4 icosahedral lattice. The genomic DNA is located inside the T = 4 shell and is the component of the innermost layer of the full capsids. The outer and intermediate layers interact in such a way that the channels along their icosahedral two-fold axis coincide and form a direct pathway between the DNA and the environment outside the capsid.  相似文献   
10.
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