全文获取类型
收费全文 | 24400篇 |
免费 | 1953篇 |
国内免费 | 1097篇 |
专业分类
27450篇 |
出版年
2024年 | 57篇 |
2023年 | 246篇 |
2022年 | 618篇 |
2021年 | 976篇 |
2020年 | 657篇 |
2019年 | 820篇 |
2018年 | 939篇 |
2017年 | 659篇 |
2016年 | 1033篇 |
2015年 | 1412篇 |
2014年 | 1607篇 |
2013年 | 1768篇 |
2012年 | 2177篇 |
2011年 | 1883篇 |
2010年 | 1196篇 |
2009年 | 1048篇 |
2008年 | 1379篇 |
2007年 | 1179篇 |
2006年 | 1056篇 |
2005年 | 934篇 |
2004年 | 812篇 |
2003年 | 728篇 |
2002年 | 630篇 |
2001年 | 436篇 |
2000年 | 385篇 |
1999年 | 367篇 |
1998年 | 233篇 |
1997年 | 183篇 |
1996年 | 148篇 |
1995年 | 149篇 |
1994年 | 117篇 |
1993年 | 103篇 |
1992年 | 173篇 |
1991年 | 153篇 |
1990年 | 143篇 |
1989年 | 109篇 |
1988年 | 86篇 |
1987年 | 88篇 |
1986年 | 69篇 |
1985年 | 84篇 |
1984年 | 49篇 |
1983年 | 42篇 |
1982年 | 37篇 |
1979年 | 45篇 |
1978年 | 36篇 |
1977年 | 30篇 |
1976年 | 38篇 |
1975年 | 34篇 |
1974年 | 31篇 |
1972年 | 30篇 |
排序方式: 共有10000条查询结果,搜索用时 25 毫秒
31.
Novobiocin blocks the Drosophila heat shock response 总被引:12,自引:0,他引:12
32.
epsilon-Crystallin, a novel avian and reptilian eye lens protein 总被引:4,自引:0,他引:4
S O Stapel A Zweers H J Dodemont J H Kan W W de Jong 《European journal of biochemistry》1985,147(1):129-136
Gel filtration of Peking duck eye lens proteins reveals a component eluting just behind delta-crystallin and comprising approximately 10% of the total soluble protein. The native Mr of this additional component is estimated to be 120000; it appears to be composed of three identical chains of Mr 38000 and pI 7.5. Circular dichroic spectroscopy showed a relatively high alpha-helical content. No immunological cross-reactivity is found with alpha-, beta-, gamma- or delta-crystallins, and partial amino acid sequence determinations likewise failed to reveal any similarity with other known crystallins. We conclude that this protein represents another and novel family of eye lens proteins, for which we propose the designation epsilon-crystallin. epsilon-Crystallin is translated from a 1450-base mRNA, which has been partially purified. epsilon-Crystallin is found scattered among avian and reptilian taxa, but not in other vertebrates. Its rate of evolutionary change seems to be as slow as that of alpha- and beta-crystallins. 相似文献
33.
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
34.
Wim R. Klein Peter A. Steerenberg Fred Poelma Elly v. d. Wiel Victor P. M. G. Rutten Wim Misdorp Wim H. de Jong E. Joost Ruitenberg 《Cancer immunology, immunotherapy : CII》1986,22(2):87-94
Summary Lymphocyte stimulation with Con A and specific immune reactivity to BCG (antibody formation to BCG and DTH reaction to PPD) were determined in BCG-treated, surgically treated and untreated cows with ocular squamous cell carcinoma. In tumor-bearing cows the Con A-induced proliferation of lymphocytes was reduced when compared to healthy controls. This suppression consisted of a reduced blastogenic response to Con A of lymphocytes from tumor-bearing cows, and the presence of a factor in the sera of these animals, as these sera suppressed the blastogenic response of lymphocytes from healthy cows. BCG had only a minor influence on the suppressive activity. Antibodies to BCG were demonstrated in 50% of the BCG-treated animals. The formation of antibodies was not influenced by intradermal injection of PPD of Mycobacterium bovis. Absorption of a BCG antibody containing serum with BOSCC tumor extracts did not reveal the existence of cross reacting antigens between BCG and BOSCC. Pretherapeutic and posttherapeutic Con A reactivity could not be correlated with clinical response. Of the 30 BCG treated cows 29 developed a positive DTH reaction to PPD. Correlation between clinical response and immune reactivity was seen only with regard to the DTH reaction to PPD: this reaction remained positive for a longer period after treatment in animals with a favorable clinical outcome than in nonresponding animals.Animals were maintained under the guidelines laid down by the Faculty of Veterinary Medicine, State University, Utrecht, The NetherlandsGrant recipient of the Koningin Wilhelmina Fonds (Netherlands Cancer Foundation)
Abbreviations used: BCG, Bacillus Calmette-Guerin; BOSCC, bovine ocular squamous cell carcinoma PBL peripheral blood leukocytes; PPD, purified protein derivative of Mycobacteria; DTH, delayed type hypersensitivity Con A, concanavalin A; PHA, phytohemagglutinin; PWM, pokeweed mitogen 相似文献
35.
Cracked corn was irradiated with gamma rays at 0-100 Mrad and the effects of the irradiation on sugar yield, susceptibility to enzymatic hydrolysis of starch, yeast growth, and alcohol production were studied. Gamma irradiation at 50 Mrad or greater produced a considerable amount of reducing sugar but little glucose. At lower dosages, gamma irradiation significantly increased the susceptibility of corn starch to enzymatic hydrolysis, but dosages of 50 Mrad or greater decomposed the starch molecules as indicated by the reduction in iodine uptake. About 12.5% reducing sugar was produced by amylase treatment of uncooked, irradiated corn. This amount exceeded the level of sugar produced from cooked (gelatinized) corn by the same enzyme treatment. The yeast numbers in submerged cultivation were lower on a corn substrate that was irradiated at 50 Mrad or greater compared to that on an unirradiated control. About the same level of alcohol was produced on uncooked, irradiated (10(5)-10(6) rad) corn as from cooked (121 degrees C for 30 min) corn. Therefore, the conventional cooking process for gelatinization of starch prior to its saccharification can be eliminated by irradiation. Irradiation also eliminated the necessity of sterilization of the medium and reduced the viscosity of high levels of substrate in the fermentation broth. 相似文献
36.
Myocardial xanthine oxidase/dehydrogenase 总被引:3,自引:0,他引:3
B Schoutsen J W De Jong E Harmsen P P De Tombe P W Achterberg 《Biochimica et biophysica acta》1983,762(4):519-524
High-energy phosphates in heart muscle deprived of oxygen are rapidly broken down to purine nucleosides and oxypurines. We studied the role of xanthine oxidase/dehydrogenase (EC 1.2.3.2/EC 1.2.1.37) in this process with novel high-pressure liquid chromatographic techniques. Under various conditions, including ischemia and anoxia, the isolated perfused rat heart released adenosine, inosine and hypoxanthine, and also substantial amounts of xanthine and urate. Allopurinol, an inhibitor of xanthine oxidase, greatly enhanced the release of hypoxanthine. From the purine release we calculated that the rat heart contained about 18 mU xanthine oxidase per g wet weight. Subsequently, we measured a xanthine oxidase activity of 9 mU/g wet wt. in rat-heart homogenate. When endogenous low molecular weight inhibitors were removed by gel-filtration, the activity increased to 31 mU/g wet wt. Rat myocardial xanthine oxidase seems to be present mainly in the dehydrogenase form, which upon storage at -20 degrees C is converted to the oxidase form. 相似文献
37.
Progesterone transformations as a diagnostic feature in the generaAlternaria,Stemphylium andCladosporium 总被引:1,自引:1,他引:0
Various species of the generaAlternaria, Stemphylium andCladosporium were shown to display a specific reaction characteristic for the given genus. In theAlternaria genus this is a 1-2-dehydrogenation of the A ring of the steroid molecule, inStemphylium 14α-hydroxylation and inCladosporium 7β-hydroxylation. This chemotaxonomic feature may supplement morphological and functional criteria in the taxonomy of filamentous fungi (Hyphomycetes). 相似文献
38.
The amino-acids sequence of the alphaB2 chain of bovine alpha-crystallin 总被引:16,自引:0,他引:16
F J Van Der Ouderaa W W De Jong A Hilderink H Bloemendal 《European journal of biochemistry》1974,49(1):157-168
39.
40.
Purification and characterization of beta-glucosidase of Alcaligenes faecalis 总被引:9,自引:3,他引:6 下载免费PDF全文
A cellobiose-utilizing bacterium isolated from sugar cane bagasse and identified as a strain of Alcaligenes faecalis (ATCC 21400) produced an inducible beta-glucoside-splitting enzyme. The enzyme was purified by a series of streptomycin and ammonium sulfate fractionations and by Sephadex and diethylaminoethyl column chromatography. The final preparation was purified 130-fold, with a recovery of about 10% of the initial enzyme activity. The enzyme had a wide pH range, with optimal activity at pH 6.0 to 7.0. The enzyme was stable in solution at pH 6.5 to 7.8 when kept at 30 C for 2 hr, but it was destroyed by temperatures above 55 C. At 58 and 60 C, the time required to inactivate 90% of the initial activity was 16 and 6.5 min, respectively. An activation energy of 9,500 cal/mole and a K(m) of 1.25 x 10(-4)m were obtained by using p-nitrophenyl beta-glucoside as a substrate. The K(i) value and hydrolysis of cellobiose by the enzyme indicated a high affinity of the enzyme for the cellobiose. The enzyme had its specificity on beta-glucosidic linkage and the rate of hydrolisis of glucosides depended upon the nature of the aglycon moiety. The inactivation studies showed the presence of sulfhydryl groups in the enzyme. The activity of the enzyme was easily destroyed by the Cu(++) and Hg(++) ions. The Michaelis-Menton relationship and the rate of heat inactivation indicated the presence of one type of noninteracting active site in the bacterial beta-glucosidase. Molecular weight of the enzyme was estimated by gel filtration (Sephadex G-200) and sucrose density gradient, and a value of 120,000 to 160,000 was obtained. 相似文献