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   268588篇
  免费   24204篇
  国内免费   319篇
  293111篇
  2018年   3492篇
  2017年   3320篇
  2016年   4315篇
  2015年   4728篇
  2014年   5665篇
  2013年   8112篇
  2012年   9155篇
  2011年   9852篇
  2010年   6565篇
  2009年   5612篇
  2008年   8357篇
  2007年   8392篇
  2006年   7983篇
  2005年   7431篇
  2004年   7292篇
  2003年   7065篇
  2002年   6831篇
  2001年   12521篇
  2000年   12559篇
  1999年   9510篇
  1998年   2892篇
  1997年   2905篇
  1996年   2839篇
  1995年   2603篇
  1994年   2536篇
  1993年   2427篇
  1992年   7321篇
  1991年   7114篇
  1990年   7160篇
  1989年   6929篇
  1988年   6443篇
  1987年   6082篇
  1986年   5405篇
  1985年   5763篇
  1984年   4541篇
  1983年   3899篇
  1982年   2731篇
  1981年   2536篇
  1980年   2344篇
  1979年   4159篇
  1978年   3175篇
  1977年   2921篇
  1976年   2859篇
  1975年   3294篇
  1974年   3532篇
  1973年   3552篇
  1972年   3080篇
  1971年   2864篇
  1970年   2548篇
  1969年   2316篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
102.
1. A phylogenetic study of oxytocin (OXT)-like immunoreactive cells was performed by the PAP method in the central nervous system of invertebrates. 2. The immunoreactivity was detected in the nerve cells of Hydra magnipapillata of the Coelenterata; Neanthes japonica and Pheretima communissima of the Annelida; Oncidium verrucosum, Limax marginatus and Meretrix lamarckii of the Mollusca; and Baratha brassica of the Arthropoda. 3. No immunoreactive cells were found in Bipalium sp. of the Platyhelminthes; Pomacea canaliculata, Aplysia kurodai, Bradybaena similaris and Achatina fulica of the Mollusca; and Gnorimosphaeroma rayi, Procambarus clarkii, Hemigrapsus sanguineus, Helice tridens and Gryllus bimaculatus of the Arthropoda; Asterina pectinifera of the Echinodermata; and Halocynthia roretzi of the Protochordata. 4. These results demonstrate that an OXT-immunoreactive substance is widely present not only in vertebrates but also in invertebrates. 5. OXT seems to have been introduced into these invertebrates at an early stage of their phylogenetic history.  相似文献   
103.
The true slime mould Physarum polycephalum was treated with various agents by spraying them upon the cell surface 4 hrs before the second synchronous mitosis. The onset of mitosis was considerably approximated after the plasmodium treatment with protein kinases from rat hepatoma or Ph. polycephalum at the late G2 phase. The catalytic and regulatory subunits of cAMP-dependent pig brain protein kinase caused retardation of mitosis, while the holoenzyme, casein kinase and alkaline phosphatase did not affect the timing of mitosis. The cyclic nucleotides and inhibitors of their metabolic enzymes were used to investigate the role of phosphorylation processes in the mitotic cycle.  相似文献   
104.
Summary Protoplasts isolated from mesophyll tissues of cauliflower (Brassica oleraceavar. botrytis) were induced to divide in culture, with 2% of them producing calli. Upon transfer to a regeneration medium containing a low auxin/cytokinin balance (0.02mg/l 1-naphthaleneacetic and 2mg/l 6-benzylaminopurine), they displayed an extensive production of hairy roots before the regeneration of shoots. Negative effects of root differentiation on the subsequent caulogenesis by such calli were not observed, since 97% of the calli regenerated hairy roots and 93% gave shoots.Abbreviations NAA 1-naphthaleneacetic acid - BAP 6-benzylaminopurine - 2,4 D 2,4-dichlorophenoxyacetic acid - GA3 gibberellic acid - MES 2-N-morpholinoethane sulfonate  相似文献   
105.
106.
Production of Enterobifidin includes the stages of preparation of culture media, reparation of lyophilizedBifidobacterium adolescentis MS-42 culture, preparation of starters, cultivation of bacteria in fermenters, biomass conservation, and its biological control. The preparation contains physiologically active bifidobacterium cells with high activities of growth = 0.7 h−1,g = 1.0 h) and acid formation (titratable acidity is ∼120–140°T; acetate concentration, 0.50–0.75%; and lactate concentration, 0.33–0.50%). The antagonistic activity of these bacteria towardsEscherichia coli 08,E. coli 086,E. coli 015,E. coli 0115, andE. coli 0101 amounts to 98.2; toProteus vulgaris 102, to 87.2; andStaphylococcus aureus 209p, to 83.2%. The bifidobacteria (with a titer of ∼109 CFU/ml) remained viable for two to five months.  相似文献   
107.
The gene of Cytotoxic T Lymphocyte-associated Antigen 4 (CTLA4), a negative regulator of T lymphocytes, contains a single-nucleotide polymorphism (SNP) at position +6230A->G (ct60A->G), which has been found associated with several autoimmune diseases and appears to reduce T-cell inhibitory activity. In Ghana, West Africa, we compared the frequencies of CTLA4 +6230 A/G and 6 haplotype-tagging SNPs in 2010 smear-positive, HIV-negative patients with pulmonary tuberculosis (TB) and 2346 controls matched for age, gender and ethnicity. We found no difference in allele frequencies between cases and controls. However, +6230A and a distinct CTLA4 haplotype and a diplotype comprising the +6230A allele were significantly less frequent among cases with large opacities in chest radiographs compared to those with small ones (Pcorrected [cor] = 0.002, Pcor = 0.00045, P = 0.0005, respectively). This finding suggests that an increased T-cell activity associated with the CTLA4 +6230G allele contributes to pathology rather than to protection in pulmonary TB.  相似文献   
108.
Data on the interaction of DNA type I topoisomerases from the murine and human placenta cells with specific and nonspecific oligonucleotides of various structures and lengths are summarized. The relative contributions of various contacts between the enzymes and DNA that have previously been detected by X-ray analysis to the total affinity of the topoisomerases for DNA substrates are estimated. Factors that determine the differences in the enzyme interactions with specific and nonspecific single- and double-stranded DNAs are revealed. The results of the X-ray analysis of human DNA topoisomerase I are interpreted taking into account data on the comprehensive thermodynamic and kinetic analysis of the enzyme interaction with the specific and nonspecific DNAs.  相似文献   
109.
The use of modernized photometric accessories to a model microscope manufactured by the Leningrad Optico-Mechanical Amalgamation (USSR), as well as the practical application of innovations facilitating and standardizing research work, has made it possible to obtain objective data indicating the presence of significant, direct, linear correlation between infectious activity and the intensity of fluorescence emitted by fluorescent antibodies bound with the antigen of 11 studied variants of Japanese encephalitis virus in continuous cell lines. The study of the dynamics of fluorescence intensity permitted the objective evaluation of the previously revealed regularity in the increase of the intensity of the induced fluorescence of Japanese encephalitis antigen in continuous cell cultures.  相似文献   
110.
Experiments on the laboratory cultures of lice infected by Weigl's method revealed that the spontaneous, erythromycin-resistant mutant of R. prowazekii strain E, adapted to the vector's organism, retained its resistance to erythromycin during 50 successive passages without the maintenance concentrations of this antibiotic. The above strain remained sensitive to tetracycline and levomycetin. Its level of sensitivity to the latter antibiotics was similar to that of R. prowazekii strains cultivated in the vector's organism for a long time.  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