全文获取类型
收费全文 | 8680篇 |
免费 | 555篇 |
国内免费 | 1篇 |
出版年
2023年 | 25篇 |
2022年 | 80篇 |
2021年 | 120篇 |
2020年 | 90篇 |
2019年 | 115篇 |
2018年 | 189篇 |
2017年 | 137篇 |
2016年 | 255篇 |
2015年 | 367篇 |
2014年 | 437篇 |
2013年 | 644篇 |
2012年 | 744篇 |
2011年 | 681篇 |
2010年 | 454篇 |
2009年 | 393篇 |
2008年 | 575篇 |
2007年 | 502篇 |
2006年 | 476篇 |
2005年 | 435篇 |
2004年 | 463篇 |
2003年 | 441篇 |
2002年 | 427篇 |
2001年 | 81篇 |
2000年 | 73篇 |
1999年 | 66篇 |
1998年 | 84篇 |
1997年 | 74篇 |
1996年 | 72篇 |
1995年 | 63篇 |
1994年 | 72篇 |
1993年 | 58篇 |
1992年 | 61篇 |
1991年 | 42篇 |
1990年 | 30篇 |
1989年 | 33篇 |
1988年 | 26篇 |
1987年 | 22篇 |
1986年 | 15篇 |
1985年 | 24篇 |
1984年 | 28篇 |
1983年 | 34篇 |
1982年 | 26篇 |
1981年 | 37篇 |
1980年 | 29篇 |
1979年 | 24篇 |
1978年 | 11篇 |
1977年 | 21篇 |
1976年 | 7篇 |
1975年 | 15篇 |
1974年 | 16篇 |
排序方式: 共有9236条查询结果,搜索用时 31 毫秒
91.
A novel chromatin-forming histone H1 homologue is encoded by a dispensable and growth-regulated gene in Bordetella pertussis 总被引:5,自引:1,他引:4
92.
93.
G Licata R Scaglione M A Dichiara G Parrinello G Capuana D Di Vincenzo 《Bollettino della Società italiana di biologia sperimentale》1984,60(10):1863-1869
The authors studied total and free circulating thyroid hormones, rT3, TBG and TSH behaviour on chronic liver disease in 11 subjects with cirrhosis of the liver with ascites(C.E.) and in 6 subjects with chronic active hepatitis (E.C.A.) in comparison with 15 healthy and euthyroid controls. Serum T3,FT3,T4 and FT4 levels were decreased significantly and serum rT3 values increased significantly both in the subjects with C.E. and in patients with E.C.A. Moreover no significantly changes of TSH and TBG levels has been found in 3 groups studied. These data suggest that the alteration of circulating thyroid hormones in chronic liver disease, may represent a compensatory way of reducing the patient's metabolic requirements. 相似文献
94.
Abstract Sunflower plants were inoculated with a virulent isolate of Sclerotinia sclerotiorum and with the same isolate nutritionally conditioned to produce small amounts of oxalic acid. The preconditioned isolate behaved as hypovirulent. Tomato plants were inoculated with four S. sclerotiorum isolates of increasing virulence. A close correlation among disease severity, accumulation of oxalic acid, decrease in pH and inhibition of polyphenoloxidase in both infected host tissues was demonstrated. Oxalic acid production as an important factor of virulence in S. sclerotiorum is emphasized and its effect on the phenolic metabolism of the host via inhibition of polyphenoloxidase is suggested. 相似文献
95.
Mario De Rosa Salvatore De Rosa Agata Gambacorta Maria Cartenì-Farina Vincenzo Zappia 《The Biochemical journal》1978,176(1):1-7
A spontaneous mutant of Escherichia coli (strain AB2847), selected for resistance to the aminoglycoside antibiotic neamine, shows severe restriction of amber suppressors in vivo. Ribosomes isolated from the mutant exhibit only low misreading in vitro in the presence of the antibiotic. Genetic and biochemical analyses indicate that the neamine-resistant phenotype is the result of two distinct mutations. The first, res3128, appears to affect the gene (strA) coding for the ribosomal protein S12. Although it leads to a restrictive phenotype it does not, however, confer resistance to streptomycin. The second mutation, X3128, is located between the sirA and AROB loci and is lethal when segregated from the res3128 mutation. It may affect the ribosome at the level of a post-translational modification. 相似文献
96.
Anna Maria Di Giulio Giovanni B. Picotti Andrea M. Cesura Alberto E. Panerai Paolo Mantegazza 《Life sciences》1982,30(19):1605-1614
Picogram amounts (50–150 pg/mg protein) of immunoreactive met-enkephalin material (met-enkephalin in IR) were detected by radioimmunoassay in human, rat and rabbit platelets. Characterization of this material by thin-layer chromatography, gel filtration chromatography and high-pressure liquid chromatography indicated that it behaves identically with synthetic met-enkephalin. No high molecular weight met-enkephalin IR could be detected in the platelet extracts, even after trypsin hydrolysis, using two antisera which are able to recognize some of the putative met-enkephalin precursors present in the adrenal gland or striatum. , thrombin released platelet met-enkephalin in IR concomitantly with 5-hydroxytryptamine (5-HT), suggesting a common subcellular localization, i.e. the 5-HT storing organelles, for met-enkephalin IR and the amine. , platelet met-enkephalin IR in the Sprague-Dawley rat was affected neither by adrenalectomy nor by hypophysectomy. Thirteen- and 18-week-old spontaneous hypertensive rats (SHR) had lower platelet concentrations of met-enkephalin in IR than age matched normotensive Wistar-Kyoto rats. 相似文献
97.
Vincenzo Carelli Felice Liberatore Antonio Casini Rosanna Mondelli Alberto Arnone Italo Carelli Giuseppe Rotilio Irene Mavelli 《Bioorganic chemistry》1980,9(3):342-351
The composition and the structure of the product from the known electrochemical dimerization of the NAD+ have been conclusively demonstrated. A detailed analysis of the 1H and 13C nmr spectra has in fact led to the conclusion that the product contains three diastereoisomeric dimers of the 4,4′-tetrahydrobipyridyl type. Furthermore, the cytoplasmic fraction obtained from a standard mitochondrial preparation of rat liver has been shown to catalyze the oxygen uptake by the dimers. A 1 : 1 molar ratio of the reagents in the redox process is indicated by manometric data on oxygen uptake complemented by spectrophotometric analysis of the oxidized substrates, suggesting that H2O2 is the reduction product. NAD+ was identified as the oxidation product by an enzymatic method. 相似文献
98.
Ettore Benedetti Benedetto Di Blasio Vincenzo Pavone Carlo Pedone Claudio Toniolo Gian Maria Bonora 《International journal of biological macromolecules》1980,2(4):217-224
The X-ray diffraction and i.r. absorption conformational analysis of has showed the absence of intramolecularly hydrogen-bonded peptide conformations in the solid state. The molecules are held together in rows of ‘cyclic dimer’ motifs through intermolecular NH … OC (acid) and OH … OC {urethane} hydrogen bonds, the secondary amide-like group of the urethane moiety being in the unusual cis conformation, whereas the carboxylic acid group in the common syn conformation. The two molecules in the unit cell present a centrosymmetric set of ?, ψ1, and ψ2 values. In polar solvents solvated species largely predominate. In saturated hydrocarbon solution non-associated and associated (mostly involving the carboxylic acid CO as the proton acceptor) species simultaneously occur. The extent of association decreases with dilution. The amount of intramolecularly hydrogen-bonded oxy-C7 and C5 forms if any, should be extremely small. The type of association at saturation seems to differ from that found in the crystalline compound obtained by precipitation with saturated aliphatic hydrocarbons (from a diethyl ether solution). 相似文献
99.
Etiolated maize leaves (Zea mays L.) contain a major isozyme of NADP-dependent malic enzyme (L-malate dehydrogenase, decarboxylating, EC 1.1.1.40) having an isoelectric point of 5.28±0.03, a Km (L-malate) 0.3–0.6 mM at pH 7.45; a broad pH optimum around pH 6.9 under the conditions of assay; a molecular weight of 280,000 (sometimes accompanied by a minor component of 150,000); and an NAD-dependent activity about 1/50 the NADP-dependent activity. This isozyme, resembling the NADP-malic enzyme of vertebrates, is labeled type 1. The dominant isozyme of young green leaves (type 2) has, however, a pI 4.90±0.03, a Km (L-malate) 0.10–0.15 mM, a pH optimum of 8, and a molecular weight of 280,000. It is also more stable and exhibits an appreciable NAD-dependent activity (1/5–1/7 the NADP activity). Both isozymes show linear kinetics, dependence on Mn or Mg ions, similar Km (NADP+), and the typical increase of Km for L-malate with increasing pH values. Type 1 isozyme of maize is assumed to be cytosolic. Type 2 corresponds in each property to the chloroplast enzyme of bundle-sheath cells. It is present at a low level in etiolated leaves and develops to a high specific activity (up to 100 nmol min-1 mg protein-1 by 150 h illumination) during photosynthetic differentiation, replacing the type 1 form.Abbreviation MES
2 (N-morpholino)ethane sulfonic acid
Work supported by grants from the Consiglio Nazionale delle Ricerche for years 1975 and 1976 相似文献
100.
Champa Sengupta Vincenzo Deluca David S. Bailey Desh Pal S. Verma 《Plant molecular biology》1981,1(1):19-34
The synthesis and processing of the major storage proteins in soybean cotyledons was studied both in vivo and in vitro. The and subunits of 7S as well as the 11S proteins are synthesized as higher molecular weight-precursors on membrane-bound polysomes. The initial translation products of the 7S are proteolytically cleaved during translation suggesting the removal of a signal peptide as evidenced by the presence of 2 and 2 peptides immunoreactive with 7S antibody in the in vitro chain completion products of the membrane-bound polysomes. This is followed or accompanied by cotranslational glycosylation, which increases their size equivalent to that of initially-synthesized precursors. In vivo pulse-labelled 7S and products are of slightly higher molecular weights than the immunoprecipitable chain-completion products, indicating further post-translational modifications. A slow post-translational processing during a period of 1.5 to 16 h yields the final 7S and glycoproteins.Acidic and basic subunits of the 11S protein appear to be synthesized from common large molecular weight (60K-59K) precursors. Antibodies to the 11S acidic component recognize both acidic and basic domains in the precursor while those raised against basic subunits appear to be specific for that region only. The processing of the 11S precursor is also very slow and occurs post-translationally. This slow rate of processing, coupled with a temporal difference in the synthesis of 7S and 11S components, suggests a highly coordinated mechanism for synthesis and packaging of these proteins into protein bodies during seed development. 相似文献