全文获取类型
收费全文 | 6805篇 |
免费 | 319篇 |
国内免费 | 282篇 |
出版年
2024年 | 11篇 |
2023年 | 79篇 |
2022年 | 151篇 |
2021年 | 160篇 |
2020年 | 222篇 |
2019年 | 317篇 |
2018年 | 318篇 |
2017年 | 205篇 |
2016年 | 211篇 |
2015年 | 171篇 |
2014年 | 430篇 |
2013年 | 686篇 |
2012年 | 202篇 |
2011年 | 413篇 |
2010年 | 235篇 |
2009年 | 290篇 |
2008年 | 297篇 |
2007年 | 320篇 |
2006年 | 267篇 |
2005年 | 279篇 |
2004年 | 250篇 |
2003年 | 223篇 |
2002年 | 186篇 |
2001年 | 113篇 |
2000年 | 86篇 |
1999年 | 95篇 |
1998年 | 86篇 |
1997年 | 109篇 |
1996年 | 110篇 |
1995年 | 84篇 |
1994年 | 69篇 |
1993年 | 71篇 |
1992年 | 67篇 |
1991年 | 54篇 |
1990年 | 29篇 |
1989年 | 43篇 |
1988年 | 27篇 |
1987年 | 35篇 |
1986年 | 31篇 |
1985年 | 34篇 |
1984年 | 77篇 |
1983年 | 44篇 |
1982年 | 56篇 |
1981年 | 31篇 |
1980年 | 32篇 |
1979年 | 31篇 |
1978年 | 11篇 |
1977年 | 19篇 |
1976年 | 12篇 |
1974年 | 15篇 |
排序方式: 共有7406条查询结果,搜索用时 15 毫秒
71.
Optimization of biolistic method for transient gene expression and production of agronomically useful transgenic Basmati rice plants 总被引:4,自引:0,他引:4
We have developed a reproducible biolistic procedure for the efficient transformation of embryogenic suspension cells of an improved aromatic Indica rice variety, Pusa Basmati 1. The -glucuronidase gene was used to assay transient transformation; other plasmids carrying either a potato protease inhibitor 2 (Pin2) gene, or a late embryogenesis-abundant protein (LEA3) gene from barley, were used for the optimization of biolistic process and transgenic plant production. After optimization of the procedure, over 600 transient transformants and at least five fertile plants showing integrative transformation were obtained per bombarded filter. At least 30% of the plants were derived from independent transformation events. The new improved procedure involves the use of a reporter gene or other useful genes driven by the strong rice actin 1 gene (Act1) promoter, osmotic pre-conditioning of cells for 24 h on medium supplemented with 0.25 M mannitol prior to bombardment, use of gold particles for DNA delivery, and use of plant regeneration medium with high (1.0%) agarose concentration. 相似文献
72.
肝再生的调控及原癌基因表达 总被引:4,自引:0,他引:4
肝脏再生过程中受到多种体液因素的调控。肝细胞生长因子(HGF)、肝刺激因子(HSS)等对肝细胞有促分裂作用;转化生长因子β1(TGFβ1)等则具有抑制作用。此外,肝再生还需要去甲肾上腺素(NE)、胰岛素等辅助分裂原的存在,共同调节肝再生。肝细胞分裂增殖与原癌基因表达密切相关。肝细胞从静息期进入细胞周期,以及在整个细胞周期中,某些原癌基因有特征性的表达。 相似文献
73.
Umesh C. Haldar Sanat K. Saha Ronald C. Beavis Nirmal K. Sinha 《Journal of Protein Chemistry》1996,15(2):177-184
Two trypsin inhibitors, LA-1 and LA-2, have been isolated from ridged gourd (Luffa acutangula Linn.) seeds and purified to homogeneity by gel filtration followed by ion-exchange chromatography. The isoelectric point is atpH 4.55 for LA-1 and atpH 5.85 for LA-2. The Stokes radius of each inhibitor is 11.4 å. The fluorescence emission spectrum of each inhibitor is similar to that of the free tyrosine. The biomolecular rate constant of acrylamide quenching is 1.0×109 M–1 sec–1 for LA-1 and 0.8 × 109 M–1 sec–1 for LA-2 and that of K2HPO4 quenching is 1.6×1011 M–1 sec–1 for LA-1 and 1.2×1011M–1 sec–1 for LA-2. Analysis of the circular dichroic spectra yields 40%-helix and 60%-turn for La-1 and 45%-helix and 55%-turn for LA-2. Inhibitors LA-1 and LA-2 consist of 28 and 29 amino acid residues, respectively. They lack threonine, alanine, valine, and tryptophan. Both inhibitors strongly inhibit trypsin by forming enzymeinhibitor complexes at a molar ratio of unity. A chemical modification study suggests the involvement of arginine of LA-1 and lysine of LA-2 in their reactive sites. The inhibitors are very similar in their amino acid sequences, and show sequence homology with other squash family inhibitors. 相似文献
74.
Trypsin-subtilisin inhibitor from marine turtle eggwhite refolded quantitatively from its fully reduced state atpH 8.5 in the presence of reduced and oxidized glutathione. The refolding process was studied by following the accompanying changes in inhibitory activity, fluorescence, sulfhydryl group titer, and hydrodynamic volume. The refolding process followed second-order kinetics with rate constants of 4.80×102 M–1 sec–1 for trypsin-inhibiting domain and 0.77× 102 M–1 sec–1 for subtilisin-inhibiting domain of the inhibitor at 30°C and their respective activation energies of the refolding process were 15.9 and 21.6 kcal/mol. Fluorescence intensity of the reduced inhibitor decreased with time of refolding until it corresponded to the intensity of the native inhibitor. The inhibitor contained 1–2%-helix, 40–42%-sheet, and 57–58% random coil structure. Refolded inhibitor gave a circular dichroic spectrum identical to that of the native inhibitor. A number of principal intermediates were detected as a function of the refolding time. Size-exclusion chromatography separated the intermediates differing in hydrodynamic volume (Stokes radius). The Stokes radius ranged from 23 Å (fully reduced inhibitor) to 18.8 Å (native inhibitor). Results indicated the independent refolding of two domains of the inhibitor and multiple pathways of folding were followed rather than an ordered sequential pathway. 相似文献
75.
Henning Ursula Wallukat Gerd Holtzhauer Martin 《Molecular and cellular biochemistry》1996,160(1):47-52
In primary cultures of neonatal rat heart cells we found a linear correlation between the number of L-type calcium channel-specific dihydropyridine (DHP) binding sites and spontaneous beating frequency (v).Formation of glycoproteins in tissue culture was suppressed by different inhibitors of N-glycosylation. This inhibition alters to a different extent the binding of the DHP ligand (+)-[methyl-3H]PN 200-110 and v. The most severe but reversible effect occurs at 6 g/ml tunicamycin (Bmax 45% and v 6%, resp., of control), a slight increase in Bmax at 0.1–0.5 mM castanospermine and 0.05–2.5 mM deoxymannojirimycin. The other inhibitors gave no significant alterations of Bmax. 相似文献
76.
77.
Chae Oh Lim Soo In Lee Woo Sik Chung Sung Han Park Inhwan Hwang Moo Je Cho 《Plant molecular biology》1996,30(2):373-379
A cDNA encoding a new phytocystatin isotype named BCPI-1 was isolated from a cDNA library of Chinese cabbage flower buds. The BCPI-1 clone encodes 199 amino acids resulting in a protein much larger than other known phytocystatins. BCPI-1 has an unusually long C-terminus. A BCPI-1 fusion protein expressed in Escherichia coli strongly inhibits the enzymatic activity of papain, a cysteine proteinase. Genomic Southern blot analysis revealed that the BCPI gene is a member of a small multi-gene family in Chinese cabbage. Northern blot analysis showed that it is differentially expressed in the flower bud, leaf and root. 相似文献
78.
Toshinori Nagaoka Ken-ichi Umezu Kenji Kouno Satoshi Yoshida Yukio Ishiguro Tadao Ando 《Plant Growth Regulation》1996,20(3):295-302
Water extracts of the compost produced from activated sludge and coffee residue were found to be selectively inhibitory to seed germination of some legumes. Germination rate of white clover (Trifolium repens L.), red clover (Trifolium pratense L.) and alfalfa (Medicago sativa L.) seeds were reduced to 2, 29 and 73% of the control, respectively, by water extracts of the compost (20 g l–1). However, the extracts did not show any inhibition to seed germination of sorghum (Sorghum bicolor Moench), African millet (Eleusine coracana Gaertn.), and Komatsuna (Brassica rapa L.) at the same concentration. The inhibitors in the compost extracts were separated by ion-exchange chromatography and reverse-phase high performance liquid chromatography (HPLC) and the inhibitory activities of seed germination were tested with white clover seeds. Five inhibitors were isolated and identified as 3,4-dichlorophenylacetic acid (3,4-DCP), 3,4-dichlorobenzoic acid (3,4-DCB), 3,4,5-trichlorophenylacetic acid, 3,4,5-trichlorobenzoic acid and mono-2-ethylhexylphthalate by 1H-, 13C-NMR spectroscopy and mass spectrometry. The inhibitory activities of some authentic chemicals of the inhibitors and the related compounds were compared. The results indicated that the main inhibitor in the compost could be 3,4-DCB, which was contained at the concentration of 6.58 mg kg–1 compost and showed the strongest inhibitory effect on seed germination of white clover among the tested compounds. 相似文献
79.
ADP-ribosylation reaction, that is the transfer of the ADP-ribose moiety of NAD+ to acceptor protein, is catalyzed by two classes of ADP-ribosyltransferases,i.e., poly(ADP-ribose) synthetase and mono (ADP-ribosyl)transferases. These two types differ not only in the number of transferring ADP-ribose units but also in the acceptor amino acid(s) and protein. Their in hibitors, particularly those of poly(ADP-ribose) synthetase, have been successfully employed in studies on biological functions of the enzymes and other related fields of research. Recently, we found many potent and specific inhibitors of poly-(ADP-ribose) synthetase, and broadened their chemical as well as biochemical variety. More recently, we found several potent inhibitors of arginine-specific mono(ADP-ribosyl)transferases and activators of poly(ADP-ribose) synthetase. 相似文献
80.
G. García-Casado R. Sánchez-Monge C. Lopez-Otín G. Salcedo 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1994,89(1):60-63
A new inhibitor of insect -amylase, designated RDAI-1, has been purified from rye (Secale cereale L.) endosperm. RDAI-1 is homologous to wheat homodimeric inhibitors. This homology is supported by their similar N-terminal amino-acid sequences, inhibitory activities towards amylases from Tenebrio molitor (Coleoptera) and human saliva, and aggregative properties in gel-filtration chromatography. The gene encoding RDAI-1, IdhaR1, is located on the short arm of chromosome 3R, which is homoeologous with wheat chromosome arms 3BS and 3DS, where the genes for homodimeric inhibitors have been previously mapped. 相似文献