全文获取类型
收费全文 | 42530篇 |
免费 | 3398篇 |
国内免费 | 2405篇 |
专业分类
48333篇 |
出版年
2024年 | 61篇 |
2023年 | 484篇 |
2022年 | 1137篇 |
2021年 | 1970篇 |
2020年 | 1223篇 |
2019年 | 1511篇 |
2018年 | 1418篇 |
2017年 | 1087篇 |
2016年 | 1636篇 |
2015年 | 2454篇 |
2014年 | 2883篇 |
2013年 | 3130篇 |
2012年 | 3637篇 |
2011年 | 3437篇 |
2010年 | 1972篇 |
2009年 | 1816篇 |
2008年 | 2133篇 |
2007年 | 1912篇 |
2006年 | 1643篇 |
2005年 | 1469篇 |
2004年 | 1232篇 |
2003年 | 1092篇 |
2002年 | 951篇 |
2001年 | 858篇 |
2000年 | 743篇 |
1999年 | 724篇 |
1998年 | 441篇 |
1997年 | 469篇 |
1996年 | 448篇 |
1995年 | 395篇 |
1994年 | 384篇 |
1993年 | 310篇 |
1992年 | 442篇 |
1991年 | 386篇 |
1990年 | 333篇 |
1989年 | 247篇 |
1988年 | 239篇 |
1987年 | 200篇 |
1986年 | 142篇 |
1985年 | 187篇 |
1984年 | 128篇 |
1983年 | 110篇 |
1982年 | 80篇 |
1981年 | 66篇 |
1980年 | 57篇 |
1979年 | 74篇 |
1978年 | 70篇 |
1977年 | 57篇 |
1976年 | 50篇 |
1973年 | 51篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
131.
杂交水稻及三系在发育过程中的酯酶同工酶比较研究 总被引:7,自引:1,他引:6
刘文芳;吴文瑜;肖翊华 《武汉植物学研究》1987,5(3):267-274
本文报道了利用聚丙烯酰胺凝胶电泳技术,测定杂交水稻及三系亲本共50个组合的萌动胚、芽,不同发育时期的叶片、根、雄蕊等12个组织或器官的酯酶同工酶的结果。根据所测结果,可把杂交水稻的酯酶同工酶酶谱分为5种类型:互补型、偏父型、偏母型、同型和“杂种”酶谱。强优势组合以互补型酶谱居多,弱优势组合都是同型酶谱,“杂种”酶谱仅见于V优64的幼穗分化期叶片和V优63、汕优63的三叶期叶片中。不同器官的互补酶谱都可作为预测杂种比势,鉴定杂交稻种子的纯度和真实性以及选配新杂交组合的一个手段或依据,但以对萌动胚或幼芽的测定更有实践意义。 相似文献
132.
133.
Y. W. Han D. J. Gallagher A. G. Wilfred 《Journal of industrial microbiology & biotechnology》1987,2(4):195-200
Summary Phytase production byAspergillus ficuum was studied using solid state cultivation on several cereal grains and legume seeds. The microbial phytase was used to hydrolyze the phytate in soybean meal and cotton seed meal. Wheat bran, soybean meal, cottonseed meal and corn meal supported good fungal growth and yielded a high level of phytase when an adequate amount of moisture was present. The level of phytase production on solid substrate was higher than that obtained by submerged liquid fermentation. Higher levels of phosphorus (more than 10 mg Pi/100 g substrate) in the growth medium (static culture) inhibited phytase synthesis, and the degree of phosphorus inhibition was less apparent in semisolid medium than in liquid medium. A static cultivation on semisolid substrate produced a higher level of phytase (2-20-fold) than that obtained by agitated cultivation. The minimal amount of water required for growth and enzyme production on those substrates was about 15%, while the optimum level for phytase production was between 25 and 35% and that for cell growth was above 50%. Optimum pH for phytase production was between 4 and 6.A ficuum grew well on raw (unheated) substrate containing a minimal amount of water and produced as much phytase as on heated substrate. About half of the phytic acid in soybean meal and cottonseed meal was hydrolyzed by treatment withA. ficuum phytase. 相似文献
134.
横断山区四种湍蛙的细胞遗传学研究 总被引:5,自引:1,他引:4
通过染色体组型分析,C带(BSG技术)分析及一种简便的Ag-NORs带分析,对四川湍蛙、理县湍蛙、棕点湍蛙和棘皮湍蛙的种间关系、染色体的演化及其性染色体等问题进行了初步探讨。结果表明:(1)四川湍蛙、理县湍蛙和棕点湍蛙之间的亲缘关系较近,而它们与棘皮湍蛙的亲缘关系较远;(2)在近缘种的分化中,染色体结构异染色质的变化和臂间倒位是重要的因素之一,这在小型染色体上表现得尤为突出;(三)四川湍蛙具有在形态上分化很明显的性染色体。C带分析表明,此性染色体主要由常染色质构成,但在其Y染色体的长臂上存在明显的中间C带,推测尚处于性染色体分化的初期阶段。 相似文献
135.
Wu Ai-Zhen Sun Yu-Kun 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1986,72(5):662-664
Summary After irradiation of the virus particles of CPV, the RNA replicase associated with the virion was isolated in the form of a genome-replicase complex with DEAE-Sephadex A-25 chromatography. This complex was then treated with Triton X-100 and purified by phosphocellulose column chromatography. The RNA replicase reconstituted with the doublestranded RNA of CPV showed both the enzyme activity of RNA polymerase and methyltransferase. The single-stranded RNA could not serve as the template for the RNA replicase. The role of the RNA replicase of CPV is discussed. 相似文献
136.
Summary An on-line respiratory quotient control system has been developed for the continuous cultivation of baker's yeast. This system is based on moving identification of the microbial dynamics. The optimal dilution rate that was selected as the control variable was determined by minimizing a performance index. Without resorting to complicated microbial analysis, a simple and practical moving model is obtained by continually updating the input and output data. The experimental results indicate the satisfactory controllability of the present system and the possible extention of the proposed method to other bioprocesses. 相似文献
137.
To determine the value of serum arabinitol concentrations in clinical practice, we identified all patients at the University of Utah Medical Center for whom a serum arabinitol determination had been requested by the attending physician or housestaff to assist in the management of candidiasis. The patient populaton was divided into three categories on the basis of clinical and pathological findings: (1) superficial candidiasis, (2) possible deep, invasive candidiasis, and (3) definite, deep invasive candidiasis. Abnormal renal function was associated with elevated concentrations of serum arabinitol in proportion to the degree of renal dysfunction. Both the serum arabinitol concentration and the arabinitol/creatinine ratio were increased in the combined patient population with candidiasis relative to normal uninfected controls (p=0.06 and 0.001, respectively). However, neither of these tests reliably distinguished patients with invasive candidiasis from those with only superficial candidal disease. 相似文献
138.
Biosynthesis of Bacillus licheniformis penicillinase in Escherichia coli and in Bacillus subtilis. 总被引:5,自引:5,他引:0
Modified prepenicillinase was accumulated in both Escherichia coli and Bacillus subtilis treated with globomycin. Although the inhibitions of processings of prepenicillinase and prolipoprotein by globomycin in E. coli are qualitatively similar, they differ in the degree of inhibition at given concentrations of globomycin. The processing of prepenicillinase proceeds much more rapidly in E. coli than in B. subtilis. 相似文献
139.
The subunit structure of membrane-bound mitochondrial transhydrogenase was investigated. Chemical modification of bovine heart submitochondrial particles with the cleavable bifunctional cross-linking reagent, dithiobis(succinimidyl propionate), resulted in the formation of three dimeric "cross-link isomers" of the enzyme, identified by immunoautoradiography, that are characteristic of cross-linked purified transhydrogenase. A limited amount of cross-linking of transhydrogenase monomer to Mr = 25,000 polypeptide was also observed. At high concentration of the cross-linker, a small amount of a higher molecular weight species was formed with both purified and membrane enzyme. Reductive cleavage of the dimeric and higher molecular weight species resulted in the regeneration of transhydrogenase monomer and several other proteolytically derived fragments. It is concluded that transhydrogenase exists in the native membrane primarily as a dimeric species. 相似文献
140.
An antiserum to pure glutamate decarboxylase (GAD) when incubated with rat cortical synaptosomes in the presence of complement caused release of 33-53% of lactate dehydrogenase (LDH) and 22-41% of total GAD. In addition most of the gamma-aminobutyrate (GABA) present was released. Anti-GAD antiserum alone, or complement alone, were without action. The antiserum plus complement had no effect on noradrenaline or choline uptake, and did not release choline acetylase (ChAT). Anti-ChAT serum plus complement released 30-37% of ChAT and 10-13% of LDH. It prevented choline uptake. This serum did not produce GAD release or prevent GABA, choline or noradrenaline uptake. When cortical synaptosomes were exposed to both antisera plus complement, their actions were strictly additive. The data indicate specific lysis of GABAergic and cholinergic synaptosomal sub-populations. 相似文献