全文获取类型
收费全文 | 4497篇 |
免费 | 305篇 |
国内免费 | 1篇 |
出版年
2022年 | 14篇 |
2021年 | 51篇 |
2020年 | 27篇 |
2019年 | 36篇 |
2018年 | 49篇 |
2017年 | 36篇 |
2016年 | 84篇 |
2015年 | 126篇 |
2014年 | 144篇 |
2013年 | 218篇 |
2012年 | 237篇 |
2011年 | 225篇 |
2010年 | 156篇 |
2009年 | 150篇 |
2008年 | 257篇 |
2007年 | 241篇 |
2006年 | 230篇 |
2005年 | 237篇 |
2004年 | 246篇 |
2003年 | 251篇 |
2002年 | 245篇 |
2001年 | 143篇 |
2000年 | 150篇 |
1999年 | 119篇 |
1998年 | 48篇 |
1997年 | 43篇 |
1996年 | 50篇 |
1995年 | 47篇 |
1994年 | 55篇 |
1993年 | 38篇 |
1992年 | 73篇 |
1991年 | 71篇 |
1990年 | 52篇 |
1989年 | 50篇 |
1988年 | 55篇 |
1987年 | 47篇 |
1986年 | 58篇 |
1985年 | 40篇 |
1984年 | 30篇 |
1983年 | 43篇 |
1982年 | 35篇 |
1981年 | 27篇 |
1980年 | 26篇 |
1979年 | 29篇 |
1978年 | 21篇 |
1977年 | 23篇 |
1975年 | 23篇 |
1974年 | 15篇 |
1972年 | 13篇 |
1969年 | 20篇 |
排序方式: 共有4803条查询结果,搜索用时 31 毫秒
21.
Expression of goat alpha-lactalbumin in Escherichia coli and its refolding to biologically active protein 总被引:1,自引:0,他引:1
A cDNA encoding the mature region of goat alpha-lactalbumin and the 3'-non-coding region was fused to cDNA of the N-terminal half of porcine adenylate kinase which had been placed under the control of the tac promoter in an expression vector in Escherichia coli. In addition, a methionine codon was inserted between the two cDNAs. When the plasmid carried the full-length 3'-non-coding region, little accumulation of the fused protein was observed. However, the deletion of two-thirds of the 3'-non-coding region produced significant expression of the fused protein in E. coli strain JM105. Since goat alpha-lactalbumin contains no methionine residue, the mature goat alpha-lactalbumin was isolated by CNBr digestion of the fused insoluble protein and refolded using thioredoxin. The homogeneous and biologically active goat alpha-lactalbumin was purified by Ca2+ ion-dependent hydrophobic chromatography. 相似文献
22.
The polymerase chain reaction for Mycoplasma pulmonis 总被引:2,自引:0,他引:2
R Harasawa K Koshimizu T Uemori O Takeda K Asada I Kato 《Microbiology and immunology》1990,34(4):393-395
In vitro DNA amplification by polymerase chain reaction was examined to detect Mycoplasma pulmonis. A pair of synthetic oligonucleotide primers was constructed, and used to amplify a unique sequence of M. pulmonis DNA. Amplified products were detected by agarose gel electrophoresis and verified by blot hybridization with a synthetic oligonucleotide probe. This system detected cellular DNA of M. pulmonis but not M. arthritidis or M. neurolyticum, and thus appears to be useful for M. pulmonis diagnosis. 相似文献
23.
24.
T Suzuki I Horibe N Uchida K Ezumi K Uchida K Takeda A Tanaka Y Nishizawa K Matsumoto 《The Journal of steroid biochemistry and molecular biology》1990,37(4):559-567
Binding affinities of modified steroidal anthrasteroids, 3 beta-hydroxy-3a beta,6-dimethyl-2,3,3a,4,5,8,9,10,10a beta,11,11a beta, 11b alpha-dodecahydro-1H-cyclopenta[a]anthracene-8-one (1) and 3a beta,6-dimethyl-2,3,3a,4,5,8,9,10,10a beta,11,11a beta,11b alpha-dodecahydro-1H-cyclopenta[a]anthracene-3,8-dione (2), the steroid oxendolone and the nonsteroid AA560, for the androgen receptor (AR) of Shionogi carcinoma 115 (SC115) and their effects on the growth of SC115 were investigated in vivo and in vitro. The inhibitory effects of these compounds on testosterone 5 alpha-reductase of SC115 tissues were also measured. The relative binding affinities of these compounds were 3.17-0.03% of that of dihydrotestosterone, and their rank order was (1) greater than AA560 greater than oxendolone much greater than (2). In the presence of 10(-9) M testosterone, anthrasteroids and AA560 inhibited the growth of SC115 cells at 10(-7) M in a serum-free medium, but oxendolone did not. In the absence of testosterone, (1), (2) and oxendolone promoted cell growth at 10(-6), 10(-7) and 10(-7) M, respectively. However, AA560 nearly completely blocked cell growth at 10(-5) M. At a 2 mg daily dose for 13 days, (1) and AA560 powerfully inhibited tumor growth in castrated DS mice treated with testosterone propionate but oxendolone had almost no effect. Anthrasteroids and oxendolone showed weak but significant agonistic activity in vivo. Anthrasteroids markedly inhibited 5 alpha-reductase activity of SC115, oxendolone weakly and AA560 not at all. The remarkable antiandrogenic activities of (1) and AA560 may partially result from their higher affinities for the AR of SC115 but other yet unknown mechanisms may also contribute to these activities. 相似文献
25.
Primary, first and second passaged endothelial cells from bovine aorta were grown in plastic culture dishes or on glass coverslips. The cells were characterized by their monolayer cobblestone appearance at confluence, their immunofluorescent staining for factor VIII-related antigen, their specific uptake of low density lipoprotein and by their ultrastructure. Following stimulation of the cells by atriopeptin II or sodium nitroprusside, both cellular and extracellular cyclic GMP levels were measured. Cellular cyclic GMP content was increased greatly by atriopeptin II in a time-dependent manner while sodium nitroprusside was essentially without effect. Increases in tissue cyclic GMP levels were associated with a time-dependent accumulation of the nucleotide in the extracellular compartment. Zaprinast, a specific inhibitor of cyclic GMP phosphodiesterases, did not significantly affect either basal or atriopeptin II-stimulated increases in cyclic GMP content, nor extracellular accumulation of the nucleotide. It is concluded that the cyclic GMP content of endothelial cells is not solely dependent on degradation by phosphodiesterases but also involves release of cyclic GMP into the extracellular compartment. 相似文献
26.
Tadashi Matsunaga Noriyuki Nakamura Naoko Tsuzaki Hiroyuki Takeda 《Applied microbiology and biotechnology》1988,28(4-5):373-376
Summary Among 200 strains of marine bluegreen algae isolated from the coastal areas of Japan, the marine blue-green alga Synechococcus sp. NKBG 040607 excreted glutamate at the highest rate, 82.6% of total amino acids production being glutamate. Synechococcus sp. NKBG 40607 was immobilized in calcium alginate gel. Glutamate production by immobilized cells was double that of native cells. Maximal glutamate production (25 g/cm3 gel per day) of the immobilized cells was observed under a light intensity of 144 Einstein/m2 per second at a cell concentration of 7.5 mg dry cells/cm3 gel. Immobilized cells of Synechococcus sp. can use nitrate as a nitrogen source. Immobilized marine Synechococcus sp. produced 0265 mg/cm3 gel of glutamate for 7 days in the presence of chloramphenicol. 相似文献
27.
C5 convertase of the alternative complement pathway: covalent linkage between two C3b molecules within the trimolecular complex enzyme 总被引:3,自引:0,他引:3
T Kinoshita Y Takata H Kozono J Takeda K S Hong K Inoue 《Journal of immunology (Baltimore, Md. : 1950)》1988,141(11):3895-3901
C5 convertase of the alternative C pathway is a complex enzyme consisting of three C fragments--one molecule of a major fragment of factor B (Bb) and two molecules of a major fragment of C3 (C3b). Within this C3bBbC3b complex, the first C3b binds covalently to the target surface, and Bb, which bears a catalytic site, binds noncovalently to the first C3b. In the present investigation, we studied the nature of the convertase that is assembled on E surfaces and obtained evidence that the second C3b binds directly to the alpha'-chain of the first through an ester bond rather than to the target surface. Thus, the alternative pathway C5 convertase could be described as a trimolecular complex in which Bb binds noncovalently to a covalently linked C3b dimer. We also obtained evidence that not only the second C3b but also the first C3b participates in binding C5, that is, covalently-linked C3b dimer acts as a substrate-binding site. Because of this two-site binding, the convertase has a much higher affinity for C5 than the surrounding monomeric C3b molecules. Based on this evidence, a new model of the alternative pathway C5 convertase is proposed. Covalent association of two subunits and the bivalent binding of the substrate are then common properties of the alternative and classical pathway C5 convertases. 相似文献
28.
Monoclonal antibodies to mouse complement receptor type 1 (CR1). Their use in a distribution study showing that mouse erythrocytes and platelets are CR1-negative 总被引:14,自引:0,他引:14
T Kinoshita J Takeda K Hong H Kozono H Sakai K Inoue 《Journal of immunology (Baltimore, Md. : 1950)》1988,140(9):3066-3072
mAb to murine C receptor type 1 (CR1) were produced and three of them were characterized. One antibody, designated as 8C12, immunoprecipitated a protein of 190,000 Mr from a detergent extract of surface-labeled spleen cells and stained spleen B but not T lymphocytes in fluorescent flow cytometry. It inhibited both CR1-mediated rosette formation and the cofactor activity of CR1 for factor I-mediated cleavage of C3b, suggesting that it recognizes the ligand-binding site of CR1. The two other antibodies, designated as 7G6 and 7E9, recognized different epitopes from that recognized by 8C12, and they cross-reacted with a protein of 150,000 Mr that is present in a spleen extract. The distribution of CR1 in murine hemopoietic cells was studied by binding experiments with radiolabeled 8C12 and fluorescent flow cytometry. When CR1 was not detected by 8C12 alone, the two other antibodies were used in combination with 8C12 to confirm the negative results. Almost all B lymphocytes from the spleen, lymph nodes, and peripheral blood were CR1 positive. Most of the Thy-1-positive lymphocytes from these tissues were CR1 negative. Thymus lymphocytes were also CR1 negative. Peritoneal macrophages and chemotactic factor stimulated but not unstimulated peripheral blood granulocytes were CR1 positive. In contrast to human E, mouse E were CR1 negative. This pattern of distribution was consistent with previous results obtained by rosette assays. Although mouse platelets cause immune adherence hemagglutination with C3b-bearing SRBC, they are CR1 negative. Three other lines of evidence also indicated that platelets are CR1 negative. First, no band of CR1 was demonstrated by immunoprecipitation with 8C12 of an extract of surface-labeled platelets. Second, 8C12, which inhibited rosette formation by lymphocytes, alone or in combination with 7G6 and 7E9, did not inhibit immune adherence between platelets and C3b-bearing SRBC. Third, polyclonal rabbit IgG prepared from anti-mouse CR1 antiserum did not inhibit immune adherence by platelets. These results strongly suggest that the C3b-binding factor(s) on mouse platelets is different from CR1 and that processing of C3b-bearing immune complexes in mouse blood may be mediated by a new and as yet unidentified C3b-binding factor(s). 相似文献
29.
The leaf ultrastructure of NADP-malic enzyme type C4 species possessing different anatomical features in the Cyperaceae was examined: types were the Rhynchosporoid type, a normal
Kranz type in which mesophyll cells are adjacent to Kranz cells, and Fimbristyloid and Chlorocyperoid types, unusual Kranz
types in which nonchlorophyllous mestome sheath intervenes between the two types of green cells. They show structural characteristics
basically similar to the NADP-malic enzyme group of C4 grasses, that is, centrifugally located chloroplasts with reduced grana and no increase of mitochondrial frequency in the
Kranz cells. However, the Kranz cell chloroplasts of the Fimbristyloid and Chlorocyperoid types exhibit convoluted thylakoid
systems and a trend of extensive development of peripheral reticulum, although those of the Rhynchosporoid type do not possess
such particular membrane systems. The suberized lamella, probably a barrier for CO2 diffusion, is present in the Kranz cell walls of the Rhynchosporoid type and in the mestome sheath cell walls of the other
two types, and tightly surrounds the Kranz cells (sheaths) that are the sites of the decarboxylation of C4 acids. These ultrastructural features are discussed in relation to C4 photosynthetic function. 相似文献
30.
Kunio Takeda Atsuya Shigemura Satoshi Hamada Weicheng Gu Defu Fang Katsushi Sasa Kazuaki Hachiya 《Journal of Protein Chemistry》1992,11(2):187-192
The effect of protein conformations on the reaction rate of Ellman's reagent, 5,5-dithiobis (2-nitrobenzoic acid) (DTNB) with sulfhydryl (SH) groups of proteins was examined. The stopped-flow method was applied to follow the reaction of DTNB with SH group of two proteins, bovine serum albumin (BSA) and ovalbumin (OVA), at various concentrations of guanidine hydrochloride and urea. The rates for both the proteins were faster in guanidine than in urea. The rate sharply depended on the protein conformations, which were monitored by changes of helix contents on the basis of the circular dichroism measurements. The reaction rate of DTNB with SH groups of BSA was maximal around 2 M guanidine and 5 M urea. On the other hand, the reaction rate of DTNB with OVA was maximal at 3.5 M guanidine, while it gradually increased with an increase in the urea concentration. The amount of reactive SH group participating in the reaction with DTNB was also estimated by the absorbance change at 412 nm. The magnitudes of absorbance change for the reaction with free SH groups of OVA at low concentrations of the denaturants were appreciably smaller than those for BSA with one free SH group. Most of the four SH groups of OVA might react with DTNB above 5 M guanidine, although only a part of them did even at 9 M urea. 相似文献