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   7601篇
  免费   557篇
  国内免费   6篇
  2023年   58篇
  2022年   121篇
  2021年   218篇
  2020年   143篇
  2019年   161篇
  2018年   232篇
  2017年   184篇
  2016年   299篇
  2015年   391篇
  2014年   408篇
  2013年   546篇
  2012年   646篇
  2011年   643篇
  2010年   379篇
  2009年   333篇
  2008年   445篇
  2007年   465篇
  2006年   412篇
  2005年   376篇
  2004年   318篇
  2003年   304篇
  2002年   282篇
  2001年   77篇
  2000年   59篇
  1999年   62篇
  1998年   55篇
  1997年   62篇
  1996年   38篇
  1995年   38篇
  1994年   35篇
  1993年   39篇
  1992年   30篇
  1991年   18篇
  1990年   21篇
  1989年   17篇
  1988年   24篇
  1987年   16篇
  1986年   16篇
  1985年   11篇
  1984年   30篇
  1983年   16篇
  1982年   12篇
  1981年   16篇
  1980年   14篇
  1979年   10篇
  1977年   11篇
  1976年   8篇
  1975年   11篇
  1974年   7篇
  1973年   9篇
排序方式: 共有8164条查询结果,搜索用时 15 毫秒
71.
The aquatic fungus Blastocladiella emersonii provides a system for studying the regulation of expression of regulatory (R) and catalytic (C) subunits of cAMP-dependent protein kinase (PKA). Blastocladiella cells contain a single PKA with properties very similar to type II kinases of mammalian tissues. During development cAMP-dependent protein kinase activity and its associated cAMP-binding activity change drastically. We have previously shown that the increase in cAMP-binding activity during sporulation is due to de novo synthesis of R subunit and to an increase in the translatable mRNA coding for R (Marques et al., Eur. J. Biochem. 178, 803, 1989). In the present work we have continued these studies to investigate the mechanism by which the changes in the level of kinase activity take place. The C subunit of Blastocladiella has been purified; antiserum has been raised against it and used to determine amounts of C subunit throughout the fungus' life cycle. A sharp increase in C subunit content occurs during sporulation and peaks at the zoospore stage. Northern blot analyses, using Blastocladiella C and R cDNA probes, have shown that the levels of C and R mRNAs parallel their intracellular protein concentrations. These results indicate a coordinate pretranslational control for C and R subunit expression during differentiation in Blastocladiella.  相似文献   
72.
Summary A mathematical model is proposed to explain the influence of the volume fraction of inoculum on the fermentation time and ethanol productivity in semicontinuous ethanol fermentation of sugar cane blackstrap molasses by pressed yeast.Nomenclature a, b, c, d constants, see equation (5) - Eo initial ethanol concentration - Ef final ethanol concentration - K1, K2, K3 constants, see equation (1) - P ethanol productivity - Pc calculated values of P - Pe experimental values of P - r correlation coefficient - So initial TRS concentration - Sm TRS concentration of the feeding mash - T fermentation time (average of the experimental values) - Tc calculated value of T - Te experimental value of T - TRS total reducing sugars calculated as glucose - Uo initial urea concentration - Um urea concentration of the feeding mash - V reactor working volume - Vi volume of the inoculum - volume fraction of inoculum=Vi/V  相似文献   
73.
In analysis of the repeats from the mink X Chromosome (Chr), we have identified a B2-like repetitive sequence of 195 base pairs (bp) flanked by short direct repeats of 14 bp. It contains regions homologous to the split intragenic RNA polymerase III promoter and a 3 A-rich region followed by an oligo(dA) sequence. A feature of the repeat is the presence of a perfect polypyrimidine tract 22 bp in length absent from the known Alu- and Alu-like sequences. Alignment of the mink B2-like sequence and mouse B2-consensus sequence allowed us to estimate their similarity as 55%. The repeat is present in 1–2×105 copies per mink genome and 2–4×103 copies per X Chr. In situ hybridization analysis demonstrated a similar distribution pattern of the B2-like repeat along the length of all the mink chromosomes including the X. We also observed the presence of mink B2-like hybridizable sequence in the genomes of other Carnivora species.The nucleotide sequence data reported in this paper have been submitted to EMBL Data Library and have been assigned the accession number X52381 (MVB2RPT).  相似文献   
74.
75.
This paper discusses the general methodological controversy between individual and group research approaches by comparing the main characteristics of these two methods as applied to the specific context of basic research on voluntary heart rate control. A review of the literature published over the past 19 years in this area of study shows an imbalance in the frequency of utilization of these two methods that strongly favors short-term group designs. Implications of this research tendency are discussed. The relevance and the advantages of applying the individual approach to voluntary autonomic control research are outlined. This area is particularly amenable to the individual approach because the phenomena under study seem to be characterized by, among other things, a smaller intrasubject than intersubject variability. It is suggested that the present imbalanced tendency in the choice of a research method be corrected and that researchers adopt a more flexible attitude in the choice of the best method for studying each specific problem.  相似文献   
76.
Summary We describe a reciprocal translocation (10;13) in a man, ascertained through the study of meiosis in semen, and a partial trisomy 10q in his abnormal son. The phenotypic anomalies of the partial 10q trisomy syndrome are probably due to the presence in triplicate of the region q25qter of chromosome 10.  相似文献   
77.
Nitrate, ammonia, urea, and glycine were compared as nitrogen sources for Acetabularia mediterranea. Cells grew normally in media containing nitrate or urea, while cells did not grow at all when the same amount of N was supplied as ammonium ion. The utilization of glycine remains questionable. Cells in medium without added N (NDM) increased in length and some formed reproductive caps. The whorls of vegetative cells showed considerable hypertrophy in NDM and in glycine. This hypertrophy was due to the elongation of only the first-(a1) and second- (a2) order articles. When cut, the basal portion of cells without added N regenerated new apices with whorls. The development of these whorls was inversely proportional to the NO2 concentration. Analyses showed that the intracellular nitrogen pool in young cells and regenerating bases was very small, about 1/10 of that of fully grown cells. Therefore we suggest that trace amounts of N contaminants in the medium supported growth and development, the uptake of which was facilitated by the hypertrophied whorls, under N-limited conditions.  相似文献   
78.
We have previously reported that treatment of CsA with aqueous HCl gives rise to the formation of a number of water-soluble compounds. Two of these were identified from their FAB-MS/MS spectra as open-chain nona- and decapeptides. We describe here the identification of two other main compounds deriving from the same treatment. Identification was rendered possible from the comparison of their FAB-MS/MS spectra with those of methyl and acetyl derivatives. The two compounds are water-soluble, open-chain undecapeptides corresponding to 1,11 seco-CsA and of 4,5 seco-isoCsA, respectively.  相似文献   
79.
Investigations of effective, orally active, and safe antidiabetic metallopharmaceuticals have been carried out during the last two decades. It has been reported that tungsten compounds mimic the action of insulin in intact cell systems. As insulin mimetics, the most investigated tungsten compound was sodium tungstate (ST), rarely investigated was tungstophosphoric acid (WPA), but never alanine complex of tungstophosphoric acid (WPA-A). In this study, the insulin mimetic activity of three different tungsten compounds, ST, WPA, and WPA-A, was evaluated by means of in vitro measurements of the glucose uptake and inhibition of free fatty acids release from epinephrine-treated isolated rat white adipocytes. We investigated the influence of concentration (lower and higher, 0.1 and 1.0 mM, respectively) and solvent: isotonic salt solution—saline (0.9% w/v of NaCl) and dimethyl sulfoxide (DMSO; 2% v/v), on the biological effect of tested compounds. Our experimental data showed that all of the three investigated tungsten compounds possess insulin mimetic activity in vitro on the isolated adipocytes. Influence of concentration and solvents on insulin mimetic effect for the certain tungsten compounds were: WPA was shown effect independently of concentration and solvents; higher concentration and DMSO were significant decreasing insulin mimetic effect of ST; lower concentration and saline led to decreasing effect of WPA-A. Generally, there were no differences in insulin mimetic effect of three tungsten compounds in lower concentration and dissolved in DMSO. When saline was used as solvent, it was needed higher concentration of investigated compounds to accomplish the same effect. In conclusion, our results suggest that low concentration (0.1 mM) of ST, WPA, and WPA-A dissolved in 2% DMSO could be the good candidates for in vivo investigation of their antidiabetic properties.  相似文献   
80.
The seven best known skin tension lines are presented. The directions they convey are schematically compared with those of the relaxed skin tension lines. Commentaries and discussion by the author are given in order to help the reader arrive at his or her own conclusions on which directions his or her incisions should take so as to obtain the best scarring.  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