全文获取类型
收费全文 | 727419篇 |
免费 | 61453篇 |
国内免费 | 1106篇 |
专业分类
789978篇 |
出版年
2018年 | 18005篇 |
2017年 | 16609篇 |
2016年 | 16249篇 |
2015年 | 12040篇 |
2014年 | 13843篇 |
2013年 | 19841篇 |
2012年 | 26029篇 |
2011年 | 33846篇 |
2010年 | 25901篇 |
2009年 | 20619篇 |
2008年 | 28350篇 |
2007年 | 30145篇 |
2006年 | 19541篇 |
2005年 | 18406篇 |
2004年 | 18804篇 |
2003年 | 18090篇 |
2002年 | 17406篇 |
2001年 | 27339篇 |
2000年 | 27122篇 |
1999年 | 21623篇 |
1998年 | 7529篇 |
1997年 | 7593篇 |
1996年 | 7310篇 |
1995年 | 6628篇 |
1994年 | 6660篇 |
1993年 | 6462篇 |
1992年 | 17701篇 |
1991年 | 17308篇 |
1990年 | 17130篇 |
1989年 | 17158篇 |
1988年 | 15686篇 |
1987年 | 14899篇 |
1986年 | 13793篇 |
1985年 | 14050篇 |
1984年 | 11412篇 |
1983年 | 9743篇 |
1982年 | 7239篇 |
1981年 | 6383篇 |
1980年 | 6180篇 |
1979年 | 10779篇 |
1978年 | 8345篇 |
1977年 | 7580篇 |
1976年 | 7343篇 |
1975年 | 8250篇 |
1974年 | 8823篇 |
1973年 | 8698篇 |
1972年 | 8095篇 |
1971年 | 7306篇 |
1970年 | 6278篇 |
1969年 | 6010篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Binding of ADP to beef-heart mitochondrial ATPase (F1) 总被引:1,自引:0,他引:1
1. ADP binding to beef-heart mitochondrial ATPase (F1), in the absence of Mg2+, has been determined by separating the free ligand by ultrafiltration and determining it in the filtrate by a specially modified isotachophoretic procedure. 2. Since during the binding experiments the 'tightly' bound ADP (but not the ATP) dissociates, it is necessary to take this into account in calculating the binding parameters. 3. The binding data show that only one tight binding site (Kd about 0.5 microM) for ADP is present. 4. It is not possible to calculate from the binding data alone the number of or the dissociation constants for the weak binding sites. It can be concluded, however, that the latter is not less than about 50 microM. 相似文献
992.
U. Behrens N. Fedoroff A. Laird M. Müller-Neumann P. Starlinger J. Yoder 《Molecular & general genetics : MGG》1984,194(1-2):346-347
Summary The cloning of the controlling element Ac from the wx-m7 allele of Zea mays is described. The cloned fragment carries a 4.3 kb insertion that by restriction analysis is indistinguishable from the Ac insertion in Ac wx-m9. It is located approximately 2.5 kb upstream of the Ac wx-m9 insertion.
Offprint requests to: P. Starlinger 相似文献
993.
Effects of mutation on the downfield proton nuclear magnetic resonance spectrum of the 5S RNA of Escherichia coli 总被引:4,自引:0,他引:4
The imino proton spectra of several mutants of the 5S RNA of Escherichia coli are compared with that of the wild type. Three of the variants discussed are point mutations, and the fourth is a deletion mutant lacking bases 11-69 of the parent sequence, all obtained by site-directed mutagenesis techniques. The spectroscopic effects of mutation are limited in all cases, and the differences between normal and mutant spectra can be used to make or confirm the assignments of resonances. Several new assignments in the 5S spectrum are reported. Spectroscopic differences due to sequence differences permit the products of single genes within the 5S gene family to be distinguished and their fates followed by NMR. 相似文献
994.
Isolation and characterization of an insulin-degrading enzyme from Drosophila melanogaster 总被引:3,自引:0,他引:3
An insulin-degrading enzyme (IDE) from the cytoplasm of Drosophila Kc cells has been purified and characterized. The purified enzyme is a monomer with an s value of 7.2 S, an apparent Km for porcine insulin of 3 microM, and a specific activity of 3.3 nmol of porcine insulin degraded/(min.mg). N-Terminal sequence analysis of the gel-purified enzyme gave a single, serine-rich sequence. The Drosophila IDE shares a number of properties in common with its mammalian counterpart. The enzyme could be specifically affinity-labeled with [125I]insulin, has a molecular weight of 110K, and has a pI of 5.3. Although Drosophila Kc cells grow at room temperature, the optimal enzyme activity assay conditions parallel those of the mammalian IDE: 37 degrees C and a pH range of 7-8. The Drosophila IDE activity, like the mammalian enzymes, is inhibited by bacitracin and sulfhydryl-specific reagents. Similarly, the Drosophila IDE activity is insensitive to glutathione as well as protease inhibitors such as aprotinin and leupeptin. Insulin-like growth factor II, equine insulin, and porcine insulin compete for degradation of [125I]insulin at comparable concentrations (approximately 10(-6) M), whereas insulin-like growth factor I and the individual A and B chains of insulin are less effective. The high degree of evolutionary conservation between the Drosophila and mammalian IDE suggests an important role for this enzyme in the metabolism of insulin and also provides further evidence for the existence of a complete insulin-like system in invertebrate organisms such as Drosophila. 相似文献
995.
996.
K P Zimmer J Caselitz G Seifert 《Virchows Archiv. B, Cell pathology including molecular pathology》1985,49(2):161-173
Epithelial cells from various sites and at various stages of differentiation reveal distinct cytokeratin polypeptide patterns. WE have localized these heterogeneous elements at the subcellular level in human salivary glands and in a solid tumor of the breast using a monoclonal and a polyclonal antibody against cytokeratin, and an antibody against tissue polypeptide antigen (TPA) which seems to be related to some cytokeratins. Labeling by the cytokeratin antibodies was more intense in squamous and duct cells than in acinar cells. The TPA:B1 antibody reacted predominantly with duct cells and to a lesser extent with acinar and squamous cells. A precise evaluation of the labeling pattern and a well-preserved cell structure appeared to be important factors in obtaining more detailed information about intermediate filament proteins. The cryoultramicrotomy and the protein A-gold technique are suitable for these studies. 相似文献
997.
The Rd gene is expressed in the livers and oviducts of laying hens and codes for the riboflavin-binding protein (RfBP) of egg yolk and egg white. A lambda gt11 cDNA library derived from chicken oviduct poly(A)+ RNA was screened with polyclonal rabbit antiserum to chicken RfBP. Positive clones were isolated and rescreened with a mixed oligonucleotide probe corresponding to residues 20-25 of the mature protein. The largest cDNA clone (969 base pairs) was subcloned into plasmid pIBI21, and the nucleotide sequence was determined by the dideoxynucleotide method. This clone contained the entire coding region for RfBP. The published amino acid sequence of the mature protein was confirmed. In addition, the following 17-residue signal peptide was deduced: Met-Leu-Arg-Phe-Ala-Ile-Thr-Leu-Phe-Ala-Val-Ile-Thr-Ser-Ser-Thr-Cys. Unexpectedly, the nucleotide sequence codes for 2 adjacent arginine residues at the carboxyl terminus that are not observed in the mature protein. The amino acid sequence of RfBP is homologous with bovine milk folate-binding protein. Eight of the nine pairs of cysteines involved in disulfide bonds in RfBP are conserved in folate-binding protein, as are all of the tryptophan residues. Sequence identity between homologous regions of these two vitamin-binding proteins is more than 30%. 相似文献
998.
Polyclonal antibodies prepared against each of the calcimedins were utilized to determine their tissue distribution. The immunological survey of rat tissues revealed that the levels of the 35-kDa calcimedin varied, while the amount of the 67-kDa calcimedin was relatively constant in the tissues examined. A new immunoreactive species, 52 kDa, was detected with the antibody to the 35-kDa calcimedin; this protein appears to be the predominant immunoreactive species in the tissues examined. Antibodies to the 35-kDa calcimedin were also used to compare many other calcium-binding proteins in order to determine immunological relationships. These comparisons demonstrate that the epidermal growth factor receptor/kinase substrate (p35), the src kinase substrate (pp36), and calregulin are immunologically unrelated to the calcimedins. However, it was found that the 67-kDa calcimedin and the p70 calelectrin are identical, as are the 35-kDa calcimedin and the p32.5 calelectrin. The calimedins are a subset of the chromobindins. In addition, the antibody to the 35-kDa calcimedin also cross-reacts with synexin, which may be related to the new 52-kDa immunoreactive protein identified. 相似文献
999.
Proteolytic degradation of ribosomal proteins occurs during the preparation of subunits of the cytoplasmic ribosomes of the protozoa Tetrahymena thermophila and the isolated subunits are inactive. Addition of 5 mM iodoacetamide to cell suspensions before extraction inhibits proteolytic activity and permits isolation of active subunits. The protein complements of these subunits have been characterized in two different two-dimensional electrophoretic systems, and their molecular weights have been determined. 相似文献
1000.
R McDonald J Hegenauer A Sucec P Saltman 《European journal of applied physiology and occupational physiology》1984,52(4):414-419
The effects of iron deficiency and endurance training on muscle myoglobin (Mb), body weights, and blood lactic acid concentration were studied in rats. Fifty animals were divided into four groups: anemic trained (AT), normal trained (NT), anemic sedentary (AS), and normal sedentary (NS). Following 5 weeks of dietary control, the mean hemoglobin values for the AT and AS rats were 0.013 +/- 0.002 mmol X l-1 (8.7 +/- 1.4 g X dl-1) and 0.014 +/- 0.003 mmol X l-1 (9.2 +/- 1.7 g X dl-1) respectively, and did not significantly change throughout the study. AT and NT rats were run on a motor driven treadmill 4 days/week for 6 weeks up to a pre-established time of 90 min. Following the training, body weights of the AT (157 +/- 13 g) and NT (153 +/- 13 g) rats were lower than their respective sedentary groups AS (172 +/- 9 g) and NS (176 +/- 15 g). Resting blood lactic acid concentration following training was lower in both trained groups, AT (3.3 +/- 2.0 mM) and NT (2.3 +/- 1.9 mM) compared to AS (8.2 +/- 2.6 mM) and NS (3.8 +/- 1.6 mM). Training increased Mb concentration in hearts of both the anemic and normal trained groups (AT, 0.66 +/- 0.13 mg X g-1; NT, 0.95 +/- 0.08 mg X g-1) compared to the sedentary groups (AS, 0.44 +/- 0.08 mg X g-1; NS, 0.70 +/- 0.13 mg X g-1). Only the AT rats showed an increase in skeletal muscle Mb. This study provides evidence that myoglobin may limit aerobic metabolism. 相似文献