全文获取类型
收费全文 | 5827篇 |
免费 | 359篇 |
专业分类
6186篇 |
出版年
2022年 | 65篇 |
2021年 | 109篇 |
2020年 | 70篇 |
2019年 | 84篇 |
2018年 | 125篇 |
2017年 | 110篇 |
2016年 | 179篇 |
2015年 | 265篇 |
2014年 | 272篇 |
2013年 | 440篇 |
2012年 | 500篇 |
2011年 | 441篇 |
2010年 | 252篇 |
2009年 | 260篇 |
2008年 | 318篇 |
2007年 | 335篇 |
2006年 | 287篇 |
2005年 | 286篇 |
2004年 | 278篇 |
2003年 | 271篇 |
2002年 | 236篇 |
2001年 | 50篇 |
2000年 | 49篇 |
1999年 | 54篇 |
1998年 | 60篇 |
1997年 | 38篇 |
1996年 | 54篇 |
1995年 | 35篇 |
1994年 | 55篇 |
1993年 | 26篇 |
1992年 | 44篇 |
1991年 | 39篇 |
1990年 | 36篇 |
1989年 | 29篇 |
1988年 | 29篇 |
1987年 | 21篇 |
1986年 | 22篇 |
1985年 | 25篇 |
1984年 | 38篇 |
1983年 | 21篇 |
1982年 | 32篇 |
1981年 | 26篇 |
1980年 | 26篇 |
1979年 | 14篇 |
1978年 | 27篇 |
1977年 | 18篇 |
1976年 | 21篇 |
1975年 | 21篇 |
1974年 | 13篇 |
1973年 | 18篇 |
排序方式: 共有6186条查询结果,搜索用时 11 毫秒
41.
Giuseppe Fossati Andrea Balsari Donatella Taramelli Maria Luisa Sensi Giuseppe Pellegris Maurizio Nava Giorgio Parmiani 《Cancer immunology, immunotherapy : CII》1982,14(2):99-104
Summary Peripheral blood lymphocytes (PBL) of melanoma patients were sensitized in vitro with lymphocytes of a single donor or with a pool of lymphocytes of 5–20 different donors. After 6–7 days, the cytotoxic activity of the sensitized PBL was tested against cultured autologous tumor cells and lymphocytes in a 51Cr-release assay. Tumor lysis was observed in 13 of 16 cases in which patients' PBL (Pt-PBL) were stimulated by a pool of allogeneic lymphocytes and in five out of seven cases when single sensitization was performed. In no case was lysis of autologous normal lymphocytes or blasts seen. Cultivation of Pt-PBL with irradiated autologous tumor cells never led to the induction of lymphocytes cytotoxic to melanoma cells. Lysability by pool-activated autologous Pt-PBL of fresh cryopreserved tumor cells was compared to that of short-term cultured tumor cells, and no significant differences were observed. Cold-target inhibition experiments indicated that the cytotoxicity of Pt-PBL was tumor-restricted since only autologous melanoma cells but not lymphocytes were able to inhibit the reaction. These results indicate that activation of Pt-PBL is necessary in order to elicit or amplify their antitumor activity. 相似文献
42.
Ribosomal RNA in the Axoplasm of the Squid Giant Axon 总被引:3,自引:3,他引:0
Antonio Giuditta Aroldo Cupellot † Giuseppe Lazzarini† 《Journal of neurochemistry》1980,34(6):1757-1760
43.
Brian P. Nichols Giuseppe F. Miozzari Magda van Cleemput George N. Bennett Charles Yanofsky 《Journal of molecular biology》1980,142(4):503-517
The nucleotide sequences of Serratia marcescens trpG and the corresponding regions of Escherichia coli, Shigella dysenteriae and Salmonella typhimurium trpD have been determined. Analysis of the nucleotide sequence divergence suggests the following evolutionary relationships: Serratia-[Salmonella, (Escherichia, Shigella)]. Partial reconstruction of ancestral nucleotide sequences and subsequent analysis of nucleotide substitutions show that the majority of nucleotide substitutions in the evolution of trp(G)D are transitions that result in a reduction of G + C content. Since most of the nucleotide substitutions are in the third position of codons, bias in synonymous codon usage also reflects G + C content. The trpE-trp(G)D junction in the four organisms is characterized by overlapping translation termination and initiation codons. The relative positions of trpE and trp(G)D thus became fixed in evolution before the fusion of trpG and trpD. Nucleotide sequences representing the fusion of trpG and trpD in Escherichia, Shigella and Salmonella are not more nor less divergent than other portions of the trp(G)D coding sequences. 相似文献
44.
Gianna Evelina De Medio Gianfranco Trovarelli Anders Hamberger Giuseppe Porcellati 《Neurochemical research》1980,5(2):171-179
Rabbit synaptosomes have been used to study the effect of the base-exchange reaction in membrane phospholipids on -aminobutyric acid (GABA) transport in vitro. The uptake of GABA was measured after a base-exchange reaction with ethanolamine, choline, orl-serine and after subsequent displacement of these exchanged moieties from lipid by bases of similar or different structures which were added to the synaptosomal medium. Serine incorporation stimulated GABA transport, but its displacement from membrane lipid by choline or ethanolamine induced an inhibition of GABA transport. Ethanolamine incorporation inhibited GABA transport, but its displacement by serine or choline resulted in stimulation of GABA uptake. Choline incorporation also inhibited GABA transport, although less than ethanolamine. The pool size of synaptosomal phospholipids, presumably involved in GABA uptake, accounted for 0.2 to 10% of the total content of membrane phospholipid. Thus, alteration of phospholipid compositior by exchange of the lipid hydrophilic head-groups influences the extent GABA uptake into rabbit synaptosomes. 相似文献
45.
A Garnier-Suillerot J P Albertini L Tosi 《Biochemical and biophysical research communications》1981,102(1):499-506
Co(II) interacts with bleomycin in aqueous solution, in the presence of air, to give a short lived mononuclear superoxo-Co(III) complex (I) identified previously, by Sugiura, by electron paramagnetic resonance measurements. This complex rapidly releases O2 to yield the dinuclear μ-peroxo-Co(III) complex (II), but is stabilized by the presence of DNA yielding a new superoxo long lived species (I′). The absorption and circular dichroism spectra of the three species (I,I′,II) have been characterized. 相似文献
46.
Giuseppe Bellucci Giancarlo Berti Maria Ferretti Franco Marioni Franca Re 《Biochemical and biophysical research communications》1981,102(3):838-844
The hydrolysis of (±)--3-bromo-1,2-epoxycyclohexane in the presence of rabbit liver microsomes was investigated, and found to yield, beside -3-bromocyclohexane--1,-2-diol, 2,3-epoxycyclohexanol. It was demonstrated that the latter compound was the only product of the enzymatic reaction, whereas the diol resulted from a non enzymatic hydration in the reaction medium. These data provide the first direct proof for a general base catalysis in the enzymatic epoxide hydration, previously hypothesized on the basis of several lines of indirect evidence, and disprove alternative mechanisms involving protonation of the oxirane oxygen. 相似文献
47.
Maria E. Ferioli Luisa Schiaffonati Giuseppe Scalabrino Gaetano Cairo Aldo Bernelli-Zazzera 《Journal of cellular physiology》1980,103(1):121-128
In liver cells recovering from reversible ischemia the increase in RNA synthesis by isolated nuclei is preceded by activation of ornithine decarboxylase, leading in turn to an increase in putrescine concentration. Treatment of the animals with 1,3-diaminopropane and putrescine prevents ornithine decarboxylase activation but does not hinder the enhancement of RNA synthesis in post-ischemic liver nuclei; therefore, ornithine decarboxylase activation does not seem to be a necessary prerequisite for the increase in RNA synthesis. Hypophysectomy does not prevent the post-ischemic increases of ornithine decarboxylase and RNA synthesis; but pre-treatment of the animals with cycloheximide—which has a dual effect on the activity of ornithine decarboxylase—abolishes the post-ischemic enhancement of RNA synthesis. In contrast with regenerating liver, changes in ornithine decarboxylase activity and putrescine concentrations in reversible ischemia are not associated to changes in S-adenosylmethionine decarboxylase activity and in spermine and spermidine concentrations that seem to be characteristic of tissues where increases in RNA synthesis are followed by DNA synthesis and cell multiplication. 相似文献
48.
Mario Campa Eleuterio Ferrannini Carlo Garzelli Vittorio Colizzi Giuseppe Falcone 《Current microbiology》1979,2(5):283-286
Pseudomonas aeruginosa infection depresses contact sensitivity to oxazolone in mice. To test whether an altered lymphocyte circulation plays a role
in this depression51Cr-labeled lymphocytes fromP. aeruginosa-infected and oxazolone-sensitized donors were injected intravenously into infected and sensitized recipients, and the radioactivity
uptake of several organs was determine. The controls consisted of normal mice receiving labeled lymphocytes from normal donors.
While the radioactivity recovered from the liver, spleen, and mesenteric lymph nodes was similar in the test and the control
group, significantly more radioactivity was recovered from the draining lymph nodes of infected and sensitized recipients.
The concentration of labeled lymphocytes from sensitized donors in the draining lymph nodes of sensitized recipients was 18%
greater than that of the controls but 31% lower than that of infected and sensitized animals receiving cells from infected
and sensitized donors.P. aeruginosa infection enhances lymphocyte entrapment within the draining lymph nodes of oxazolone-sensitized mice. 相似文献
49.
Derek Jones Giuseppe Disteffano Claudio Toniolo Gian Maria Bonora 《Biopolymers》1978,17(11):2703-2713
The problem of the quantitative determination of sulfoxide groups in peptide molecules has been re-examined. The approaches currently available for the estimation of δ-sulfoxide amino acids are limited in number and characterized by serious shortcomings; in addition, the choice of methods for the estimation of γ-sulfoxide amino acids is even more restricted. A new, rapid, and nondestructive direct method for determining quantitatively all types of sulfoxides in peptide molecules by using x-ray photoelectron spectroscopy is described. 相似文献
50.
Analysis of gene function of bacteriophage phi 29 of Bacillus subtilis: identification of cistrons essential for viral assembly. 总被引:23,自引:10,他引:13 下载免费PDF全文
Restrictive infection of Bacillus subtilis by suppressor-sensitive (sus) mutants of phi 29 has been used to search for cistrons that function in viral assembly. The products of cistrons 7, 9, 10, and 16 are necessary for head morphogenesis. The neck upper collar protein P10 and the tail protein P9 must be present for DNA packaging to occur. The protein P7 must be present for phage-related particles to form. A prohead-like particle has been isolated during 16-restrictive infection. The particle is composed of the proteins Hd, P10, F, and P7. P16 must function for DNA-filled particles to accumulate. A DNA-containing particle produced in the absence of the cistron 11 product may be an intermediate in the phi 29 assembly pathway. The protein P13 interacts with P9 and P11 to form a stable DNA-filled particle. The products of cistrons 2 and 3 are essential for viral DNA synthesis, and in their absence virus-related particles are not detected. 相似文献