全文获取类型
收费全文 | 11436篇 |
免费 | 870篇 |
国内免费 | 4篇 |
专业分类
12310篇 |
出版年
2022年 | 59篇 |
2021年 | 87篇 |
2020年 | 62篇 |
2019年 | 94篇 |
2018年 | 104篇 |
2017年 | 126篇 |
2016年 | 168篇 |
2015年 | 231篇 |
2014年 | 312篇 |
2013年 | 650篇 |
2012年 | 533篇 |
2011年 | 528篇 |
2010年 | 362篇 |
2009年 | 340篇 |
2008年 | 521篇 |
2007年 | 533篇 |
2006年 | 488篇 |
2005年 | 484篇 |
2004年 | 514篇 |
2003年 | 525篇 |
2002年 | 481篇 |
2001年 | 456篇 |
2000年 | 467篇 |
1999年 | 370篇 |
1998年 | 142篇 |
1997年 | 142篇 |
1996年 | 112篇 |
1995年 | 122篇 |
1994年 | 119篇 |
1993年 | 106篇 |
1992年 | 267篇 |
1991年 | 239篇 |
1990年 | 234篇 |
1989年 | 230篇 |
1988年 | 226篇 |
1987年 | 187篇 |
1986年 | 197篇 |
1985年 | 166篇 |
1984年 | 118篇 |
1983年 | 134篇 |
1982年 | 111篇 |
1981年 | 74篇 |
1980年 | 75篇 |
1979年 | 120篇 |
1978年 | 73篇 |
1977年 | 73篇 |
1975年 | 55篇 |
1973年 | 61篇 |
1972年 | 53篇 |
1970年 | 50篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
71.
Characterization of dehydropeptidase I in the rat lung 总被引:1,自引:0,他引:1
T Hirota Y Nishikawa M Tanaka T Igarashi H Kitagawa 《European journal of biochemistry》1986,160(3):521-525
The activity of dehydropeptidase I in rat tissues decreases in the order of lung greater than kidney greater than liver-spleen greater than other tissues, while aminopeptidase activity is high in the kidney, and lower in the lung than in other tissues. Dehydropeptidase I was solubilized from the membrane fraction of rat lung by treatment with papain and purified by DEAE-cellulose column chromatography, affinity chromatography on concanavalin-A-Sepharose and high-performance liquid chromatography gel filtration. The purified preparation was found to be homogeneous on sodium dodecyl sulfate/polyacrylamide gel electrophoresis. The relative molecular mass was estimated to be 150,000 by gel filtration, comprising a homodimer of two 80,000-Mr subunits. The enzyme activity was inhibited by cilastatin, o-phenanthroline and ATP. This enzyme catalyzed the hydrolysis of S(substituent)-L-cysteinyl-glycine adducts such as L-cystinyl-bis(glycine) and N-ethylmaleimide-S-L-cysteinyl-glycine, as well as the conversion of leukotriene D4 to E4. Furthermore it catalyzed a hydrolytic splitting of L-Leu-L-Leu, but not S-benzyl-L-cysteine p-nitroanilide, which is a good substrate for aminopeptidase. Our enzyme preparation was immunologically identical to the rat renal dehydropeptidase I. The physiological significance of the pulmonary dehydropeptidase I on the metabolism of glutathione and its adducts is discussed. 相似文献
72.
The agglutinability-masking factors (AMFs) of a and mating types of Issatchenkia scutulata var. scutulata were prepared from culture fluids. AMFs masked the agglutinability of opposite mating-type cells sex-specifically, just like agglutination substances responsible for sexual cell agglutination. a AMF adsorbed to cells was eluted by incubating the cells at 60°C for 10 min. AMF was prepared directly from culture fluids of cells by DEAE-cellulose ion exchange chromatography. The active part of the AMFs is thought to be a peptidyl moiety because of the sensitivity to subtilisin. The pretreatment of cells with AMF of the opposite mating-type was shown to promote zygote formation. AMF slightly inhibited growth in a cells but not in cells, while a AMF did not show any growth-inhibitory effect on either a or x cells. 相似文献
73.
The Site of Synthesis and Accumulation of Rice Storage Proteins 总被引:12,自引:0,他引:12
Electron microscopy showed that the two types of protein bodies(PB) in starchy endosperms of rice were formed differently duringthe period of storage protein accumulation. Two routes for thetransport of storage protein from the site of synthesis at therough endoplasmic reticulum (RER) to the site of accumulationwere also proposed. PB-I, bound by a single membrane to whichribosomes were attached, was thought to develop inside the cisternaeof RER, while the PB-II membrane was thought to originate fromthe vacuole. In the wheat germ cell-free translation system, storage protein-relatedpolypeptides of developing rice endosperms, including a precursorof glutelin and putative precursors of prolamin, were directedby membrane-bound polysomes but not by free-polysomes. Immunoassayof the total translation products directed by a PB fractionshowed that 46% were storage protein-related polypeptides. Rice storage proteins (prolamin) that accumulate in PB-I appearto be synthesized by membrane-bound polysomes attached to PB-Ior RER and to pass through the membrane into the lumen wherethey aggregate and are deposited. The proteins (glutelin andglobulin) that accumulate in PB-II, however, seem to be synthesizedby membrane-bound polysomes as a large precursor and to becomesequestered into the cisternal space of RER, from where theyare transferred to the vacuolar precursor of PB-II. (Received August 6, 1985; Accepted November 6, 1985) 相似文献
74.
Lemna paucicostata 6746, a short-day plant, produced flowerbuds even under continuous light when cultured for 3 days inferricyanide containing ammonium-free medium followed by cultureon nitrogen-rich medium (either nitrate or ammonium). Dailytreatment with ferricyanide in the absence of ammonium for morethan 8 hours, which completely inhibited nitrate reductase activitywithin 6 hours after the addition to the medium, induced daylength-independentflowering even when the ammonium-rich medium was given duringthe remaining hours. The presence of ammonium for 1 hour atthe middle of the 14-h ferricyanide treatment almost completelysuppressed floral induction. (Received March 6, 1986; Accepted June 3, 1986) 相似文献
75.
A species of Daphnia, Daphnia curvirostris Eylmann, found in high mountain lakes and ponds in central Japan is described. Although there were some differences in the shape of the male rostrum and the chromosome number between European populations as described by Johnson (1952) and Trentini (1980), and Japanese ones collected from high mountain waters, Japanese specimens had many characteristics similar to the taxon D. curvirostris of Europe. 相似文献
76.
Structure of the trypsin-binding domain of Bowman-Birk type protease inhibitor and its interaction with trypsin 总被引:7,自引:0,他引:7
Y Tsunogae I Tanaka T Yamane J Kikkawa T Ashida C Ishikawa K Watanabe S Nakamura K Takahashi 《Journal of biochemistry》1986,100(6):1637-1646
The crystal structure of the complex formed by bovine trypsin and Bowman-Birk type protease inhibitor AB-I extracted from azuki beans (Vigna angularis) 'Takara' has been analyzed. The structure was solved by the application of the phase combination of single isomorphous phases and trypsin model phases, followed by phase improvement using the iterative Fourier technique. From the resulting electron density map, a three-dimensional atomic model of the trypsin binding domain of AB-I has been built. The peptide chain at the trypsin reactive site turns back sharply at Pro29 and forms a 9-residue ring (Cys24-Cys32). The 'front side' of this ring, consisting of the reactive site (Cys24-Met28), interacts with trypsin in a similar manner to other families of inhibitors and forms a stable complex, which seems to be maintained by the interactions with the 'back side' of this ring (Pro29-Cys34). The similar spatial arrangements of the 'back side' of this inhibitor and the 'secondary contact region' of the other inhibitors with respect to the reactive site suggest an important common role of these regions in exhibiting inhibitory activity. 相似文献
77.
A high molecular weight protease in the cytosol of rat liver. II. Properties of the purified enzyme 总被引:2,自引:0,他引:2
K Tanaka T Yoshimura A Ichihara K Kameyama T Takagi 《The Journal of biological chemistry》1986,261(32):15204-15207
The properties of a soluble endoprotease from rat liver were studied. The enzyme was purified in a latent form. It sedimented as a single component with a sedimentation coefficient (S(0)20,w) of 19.8 S. Measurement by quasi-elastic light scattering gave a diffusion coefficient (D(0)20,w) of 2.5 X 10(-7) cm2 X s-1 and an effective hydrodynamic radius of 85 A. The enzyme had an unusually high molecular weight, estimated as 743,000 by sedimentation equilibrium and 722,000 by sedimentation velocity and diffusion measurements and as 760,000 by a recently developed low-angle laser light scattering method. Judging from electron microscopic observation and the calculated frictional and axial ratios, the enzyme molecule is disc-shaped. Analysis of the far-ultraviolet circular dichroic spectrum showed that the enzyme contains 50% alpha-helical, 25% beta-sheet, and 15% unordered structures with 10% beta-turns. The isoelectric point of the enzyme is 5.0. These properties indicate that the purified enzyme is a homogeneous molecule. In addition, the enzyme is a simple protein since it contains no measurable amounts of nucleic acid carbohydrate or lipid. 相似文献
78.
One way in which serum promotes survival of primary cultured hepatocytes is by inhibiting plasma membrane protease (Nakamura, T., Asami, O., Tanaka, K., and Ichihara, A. (1984) Exp. Cell Res. 155, 81-91). One of these proteases was solubilized from the plasma membranes of rat liver with 4% octyl glucoside and purified to a homogeneous state by affinity chromatography on bovine pancreatic trypsin inhibitor linked to Sepharose 4B. The protease had an apparent Mr = 120,000 by Sephacryl S-200 gel filtration and the Mr of its subunits was 30,000, as determined by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate. It appeared to be a glycoprotein. A high concentration of detergent was necessary to keep the protein soluble. The purified enzyme readily hydrolyzed synthetic tripeptide nitroanilides at sites adjacent to Arg or Lys residues, but did not degrade synthetic substrates of chymotrypsin, elastase, or aminopeptidase. It showed endopeptidase activity, hydrolyzing various proteins such as casein, hemoglobin, and denatured albumin. The enzyme was strongly inhibited by diisopropyl fluorophosphate, phenylmethanesulfonyl fluoride, bovine pancreatic trypsin inhibitor, leupeptin, antipain, and alpha 1-antitrypsin, but not by chymostatin, elastatinal, or inhibitors of carboxyl, thiol, or metallo proteases, suggesting that it is a seryl trypsin-like protease. This protease was found in plasma membranes of rat and mouse liver and in small amounts in those of kidney, but not in those of brain, red cells, Ehrlich ascites tumor, or two Morris hepatomas, suggesting that it may be involved in differentiated functions of normal hepatocytes. 相似文献
79.
Tissue distribution of rat angiotensinogen mRNA and structural analysis of its heterogeneity 总被引:20,自引:0,他引:20
The tissue distribution and the structural heterogeneity of the rat angiotensinogen mRNA have been investigated with the aid of a previously cloned cDNA as well as a genomic DNA for rat angiotensinogen as analytical probes. The angiotensinogen mRNA is expressed not only in the liver but also in various tissues including the brain, kidney, adrenal gland, ovary, and lung. The relative levels of the mRNA in the above tissues have been estimated to be 3-4, 20-30 (for the next three tissues), and around 100 times less than that in the liver, respectively. The mRNAs in both hepatic and extrahepatic tissues are encoded by a single gene in the rat genome. At least four different size classes of the angiotensinogen mRNA that start with a single 5' terminus and differ only in the lengths of their 3'-untranslated regions have been identified, and these multiple mRNA species are most likely generated by using the polyadenylation signals AAUAAA and AUUAAA found 10-30 nucleotides upstream from the four polyadenylation sites. Because the structures of these multiple mRNA species do not vary among the tissues of the liver, brain, and kidney, angiotensinogen synthesized locally is structurally identical to that produced in the liver and may have some biological roles independent of the circulating angiotensinogen, mainly derived from the liver. In addition, the sequence of the 5'-flanking region of the angiotensinogen gene has been determined, and some features common to other steroid hormone-responsive genes have been discussed. 相似文献
80.
Effect of substance P on neurally mediated contraction of rabbit airway smooth muscle 总被引:8,自引:0,他引:8
The neuromodulatory action of substance P (SP) was investigated in isolated rabbit tracheal smooth muscle (TSM) segments contracted with electrical field stimulation (ES). The tissues were placed in organ baths containing modified Krebs-Ringer solution and stimulated at a constant voltage (8 V; 24.5 mA) and pulse duration (2 ms) with ES frequencies ranging from 1 to 100 Hz. In the presence of SP, there occurred a dose-dependent augmentation of the TSM contractile response to any given ES, with the maximal effect of SP obtained at a dose of 10(-7) M. Accordingly, with the administration of 10(-7) M SP, the ES frequency-response relationship was altered so that 1) the mean (+/- SE) maximal tension (Tmax) induced by ES significantly increased (P less than 0.02) from a base-line value of 273 +/- 53 to 402 +/- 45 g/g TSM; and 2) the mean (+/- SE) log ES frequency producing 50% of Tmax (ES50) significantly decreased from a base-line value of 1.278 +/- 0.069 to 1.102 +/- 0.070 Hz (P less than 0.01). In contrast to these effects on ES-induced contraction, SP administration did not affect the TSM contractile response to administered methacholine chloride (10(-8) to 10(-3) M). On the other hand, the effects of SP on ES-induced contraction were independently blocked by the cholinergic antagonist, atropine (10(-6) M); the neurotoxin, tetrodotoxin (10(-6) g/ml); and the SP antagonist, D-Arg1,D-Pro2,D-Trp7,9,Leu11-SP (10(-5) M).(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献