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271.
Hypoxanthine-guanine phosphoribosyltransferase (HGPRT, EC 2.4.2.8) from a newly characterized thermophile Thermoanaerobacter tengcongensis was expressed in Escherichia coli and purified. Analytical gel filtration suggested that the enzyme exist as a homotetramer in solution. The optimal pH for the forward reaction was found to be 8.0 and the optimal temperature 70 degrees C. The steady-state kinetic characteristics suggest that hypoxanthine is the most effective substrate. This enzyme showed a half-life of 75min at 50 degrees C and no apparent loss of activity after 3 months at 4 degrees C. 相似文献
272.
Kuo KH Herrera AM Wang L Paré PD Ford LE Stephens NL Seow CY 《American journal of physiology. Cell physiology》2003,285(2):C384-C390
Airway smooth muscle is able to adapt and maintain a nearly constant maximal force generation over a large length range. This implies that a fixed filament lattice such as that found in striated muscle may not exist in this tissue and that plastic remodeling of its contractile and cytoskeletal filaments may be involved in the process of length adaptation that optimizes contractile filament overlap. Here, we show that isometric force produced by airway smooth muscle is independent of muscle length over a twofold length change; cell cross-sectional area was inversely proportional to cell length, implying that the cell volume was conserved at different lengths; shortening velocity and myosin filament density varied similarly to length change: increased by 69.4% ± 5.7 (SE) and 76.0% ± 9.8, respectively, for a 100% increase in cell length. Muscle power output, ATPase rate, and myosin filament density also have the same dependence on muscle cell length: increased by 35.4% ± 6.7, 34.6% ± 3.4, and 35.6% ± 10.6, respectively, for a 50% increase in cell length. The data can be explained by a model in which additional contractile units containing myosin filaments are formed and placed in series with existing contractile units when the muscle is adapted at a longer length. muscle contraction; myosin filaments; ATPase activity; electron microscopy 相似文献
273.
274.
275.
The mechanical stability of ubiquitin is linkage dependent 总被引:12,自引:0,他引:12
Carrion-Vazquez M Li H Lu H Marszalek PE Oberhauser AF Fernandez JM 《Nature structural biology》2003,10(9):738-743
Ubiquitin chains are formed through the action of a set of enzymes that covalently link ubiquitin either through peptide bonds or through isopeptide bonds between their C terminus and any of four lysine residues. These naturally occurring polyproteins allow one to study the mechanical stability of a protein, when force is applied through different linkages. Here we used single-molecule force spectroscopy techniques to examine the mechanical stability of N-C-linked and Lys48-C-linked ubiquitin chains. We combined these experiments with steered molecular dynamics (SMD) simulations and found that the mechanical stability and unfolding pathway of ubiquitin strongly depend on the linkage through which the mechanical force is applied to the protein. Hence, a protein that is otherwise very stable may be easily unfolded by a relatively weak mechanical force applied through the right linkage. This may be a widespread mechanism in biological systems. 相似文献
276.
277.
盐爪爪耐盐相关基因的cDNA-AFLP分析 总被引:1,自引:0,他引:1
以不同浓度NaCl(0、100、200、300、400和500 mmol/L)处理生长了4周的盐爪爪(Kalidium foliatum),48h后取其幼嫩叶片用于RNA提取,并进行了cDNA-AFLP表达差异分析.结果表明,用256对引物扩增出连续性差异片段155条,按照NaCl浓度升高的顺序,划分为8种差异带类型,即强→弱"、弱→强"、有→无"、无→有"、有→无→有"、无→有→无"、强→弱→强"和弱→强→弱".测序后获得176个新表达序列标签(ESTs),已将长度大于100 bp的162个ESTs登录到GenBank,登录号为HO205290~HO205450.经BLAST序列比对分析发现,盐爪爪的耐盐性可能与能量、新陈代谢、防御、转运、转录和翻译等相关蛋白有关. 相似文献
278.
Salsolinol (1-methyl-6,7-dihydroxy-1,2,3,4-tetrahydroisoquinoline; Sal) is structurally similar to 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine,
which is supposed to have a role in the development of Parkinson-like syndrome in both human and non-human subjects. In the
human brain, the amount of (R)-enantiomer of Sal is much higher than (S)-enantiomer, suggesting that a putative enzyme may participate in the synthesis of (R)-salsolinol, called (R)-salsolinol synthase. In this study, the (R)-salsolinol synthase activity in the condensation of dopamine and acetaldehyde was investigated in the crude extracts from
the brains of Sprague Dawley rats. Identification of the enzymatic reaction products and enzyme activity detection were achieved
by HPLC-electrochemical detection. The discovery of this enzyme activity in rat’s brain indicates the natural existence of
(R)-salsolinol synthase in the brains of humans and rats, and it is distributed in most brain regions of rat with higher activity
in soluble proteins extracted from striatum and substantia nigra. 相似文献
279.
Haishan Tian Lu Tang Yi Wang Xiaojie Wang Lili Guan Jian Zhang Xiaoping Wu Xiaokun Li 《International journal of peptide research and therapeutics》2011,17(2):123-129
Recombinant human keratinocyte growth factor-2 (rhKGF-2) has previously been expressed in Escherichia coli using isopropyl-β-d-thiogalactopyranoside (IPTG), a non-metabolizable and expensive compound, as the inducer. In order to determine whether IPTG
could be replaced with the cheap and natural lactose to induce rhKGF-2 expression, we examined the expression of rhKGF-2 in
flask culture and 30-l fermentation using lactose as the inducer. The optimized fermentation induced with lactose resulted
in 1,382 g of cell mass, corresponding to a 84% enhancement in cell mass compared with IPTG induction. While the expression
level of rhKGF-2 induced with lactose was comparable to that induced with IPTG, the solubility of target protein was increased
by lactose induction than by IPTG induction. The recombinant protein was further purified by cation exchange and heparin-affinity
chromatography. 255 milligrams of pure rhKGF-2 was achieved per liter culture by lactose induction, 52% higher than that obtained
by IPTG induction. A preliminary biochemical characterization of purified rhKGF-2 was performed by Western blotting and mitogenic
activity analysis, and the results demonstrated that the purified lactose-induced rhKGF-2 could react with anti-human KGF-2
antibody and stimulate the proliferation of FGFR2-IIIb-transfected mouse BaF3 cells as IPTG-induced rhKGF-2 could do. 相似文献
280.