全文获取类型
收费全文 | 3997篇 |
免费 | 435篇 |
国内免费 | 5篇 |
出版年
2021年 | 58篇 |
2020年 | 43篇 |
2018年 | 55篇 |
2017年 | 47篇 |
2016年 | 75篇 |
2015年 | 105篇 |
2014年 | 119篇 |
2013年 | 168篇 |
2012年 | 149篇 |
2011年 | 168篇 |
2010年 | 125篇 |
2009年 | 94篇 |
2008年 | 156篇 |
2007年 | 149篇 |
2006年 | 125篇 |
2005年 | 128篇 |
2004年 | 123篇 |
2003年 | 120篇 |
2002年 | 130篇 |
2001年 | 125篇 |
2000年 | 113篇 |
1999年 | 98篇 |
1998年 | 53篇 |
1997年 | 46篇 |
1996年 | 55篇 |
1995年 | 56篇 |
1994年 | 46篇 |
1993年 | 42篇 |
1992年 | 69篇 |
1991年 | 83篇 |
1990年 | 77篇 |
1989年 | 67篇 |
1988年 | 65篇 |
1987年 | 62篇 |
1986年 | 55篇 |
1985年 | 57篇 |
1984年 | 52篇 |
1983年 | 45篇 |
1982年 | 36篇 |
1981年 | 45篇 |
1980年 | 40篇 |
1979年 | 45篇 |
1978年 | 45篇 |
1976年 | 38篇 |
1975年 | 53篇 |
1974年 | 63篇 |
1973年 | 38篇 |
1972年 | 38篇 |
1971年 | 52篇 |
1970年 | 38篇 |
排序方式: 共有4437条查询结果,搜索用时 15 毫秒
91.
92.
93.
94.
H B Dixon R A Giddens R A Harrison C E Henderson W E Norris D M Parker R N Perham P Slater M J Sparkes 《Journal of enzyme inhibition》1991,5(2):111-117
Acylphosphonic acids, R-CO-PO(OH)2, have been synthesized by the steps [formula: see text] of which the last is new and provides a mild method for de-esterifying acylphosphonic acids. Their reductive amination gives a simple way of making 1-aminoalkylphosphonic acids. Acetylphosphonic acid inhibited NAD+ reduction by pyruvate with the pyruvate dehydrogenases from Escherichia coli and Bacillus stearothermophilus. The inhibition was competitive with pyruvate, with Ki of 6 microM for the E. coli enzyme (pyruvate Km 0.5 mM) and one of 0.4 mM of the B. stearothermophilus enzyme (pyruvate Km 0.1 mM). Acetylphosphonate and its monomethyl ester are substates for pig heart lactate dehydrogenase, with Km values of 15 mM and 10 mM respectively (pyruvate Km 0.05 mM) and specificity constants one thousandth that for pyruvate. 相似文献
95.
96.
Structure and assembly of turnip crinkle virus. VI. Identification of coat protein binding sites on the RNA 总被引:7,自引:0,他引:7
Structural studies of turnip crinkle virus have been extended to include the identification of high-affinity coat protein binding sites on the RNA genome. Virus was dissociated at elevated pH and ionic strength, and a ribonucleoprotein complex (rp-complex) was isolated by chromatography on Sephacryl S-200. Genomic RNA fragments in the rp-complex, resistant to RNase A and RNase T1 digestion and associated with tightly bound coat protein subunits, were isolated using coat-protein-specific antibodies. The identity of the protected fragments was determined by direct RNA sequencing. These approaches allowed us to study the specific RNA-protein interactions in the rp-complex obtained from dissociated virus particles. The location of one protected fragment downstream from the amber terminator codon in the first and largest of the three viral open reading frames suggests that the coat protein may play a role in the regulation of the expression of the polymerase gene. We have also identified an additional cluster of T1-protected fragments in the region of the coat protein gene that may represent further high-affinity sites involved in assembly recognition. 相似文献
97.
Methandrostenolone dose (amount and duration) and methods of isolation from urine can influence the identification and quantitation of methandrostenolone metabolites. Long-term use of methandrostenolone at high dosages led to the appearance of unmetabolized drug in the urine and contributed to the identification of a previously unreported metabolite, 3 beta, 6 section, 17 beta-trihydroxy-17 alpha-methyl-5 section-1-androstene. Exposure of methandrostenolone in vitro to acid conditions induced a retropinacol rearrangement in the D-ring of the methandrostenolone molecule, causing the formation of 18-nor-17,17-dimethyl-1,4,13(14)-androstatrien-3-one in large amounts. The same acidic conditions led to the addition of a hydroxyl at the 6 position of the B-ring of either the retropinacol rearrangement products or native methandrostenolone resulting in the formation of 6 beta-hydroxy-18-nor-17,17-dimethyl-1,4,13(14)-androstatrien-3-one, 6 alpha- hydroxy-18-nor-17,17-dimethyl-1,4,13(14)-androstatrien, 6 beta-17 alpha-methyl-1,4-androstadien-3-one and 6 alpha,17 beta-dihydroxy-17 alpha-methyl-1,4-androstadien-3-one. Hydroxylation of native methandrostenolone at the 6 position also occurs endogenously. However, no evidence of an endogenous retropinacol rearrangement was found. Silylating agents alone can induce the formation of small amounts of 6 beta-17 beta-dihydroxy-17 alpha-methyl-1,4-androstadien-3-one. Discrepancies between previously published reports on methandrostenolone metabolism in man are discussed and compared with an animal model. 相似文献
98.
The paper considers bone-marrow repopulation experiments with injected mixtures of two types, A and B, of genetically marked donor cells. The covariance of the proportions of type A erythrocytes and lymphocytes is analysed as the sum of two components, under a stratified binomial model allowing the proportions of type A cells to vary in postulated strata of the mixture and with the assumption that the genetic marker does not influence cell development. The ratio of the two components is not experimentally estimable, but each of them has an interesting "demographic" interpretation. Possible inferences about certain "two-cell probabilities" are derived, and the experimental findings that necessitated the stratified model are illustrated. 相似文献
99.
100.
Influence of temperature on the calcium sensitivity of the myofilaments of skinned ventricular muscle from the rabbit 总被引:4,自引:1,他引:3 下载免费PDF全文
The steady-state myofilament Ca sensitivity was determined in skinned cardiac trabeculae from the rabbit right ventricle (diameter, 0.13-0.34 mm) at 36, 29, 22, 15, 8, and 1 degree C. Muscles were stimulated to 0.5 Hz and stretched to a length at which maximum twitch tension was generated. The preparation was then skinned with 1% vol/vol Triton X-100 in a relaxing medium (10 mM EGTA, pCa 9.0). Each preparation was exposed to a series of Ca-containing solutions (pCa 6.3-4.0) at two of the six temperatures studied (temperature was regulated to +/- 0.1 degree C). The pCa values (mean +/- SD, n = 6) corresponding to half maximal tension at 36, 29, 22, 15, 8, and 1 degree C were 5.47 +/- 0.07, 5.49 +/- 0.07, 5.34 +/- 0.05, 5.26 +/- 0.09, 4.93 +/- 0.06, and 4.73 +/- 0.04, respectively. Mean (+/- SD) maximum tension (Cmax) developed by the preparation as a percentage of that at 22 degrees C was 118 +/- 10, 108 +/- 5, 74 +/- 6, 57 +/- 7, and 29 +/- 5% at 36, 29, 15, 8, and 1 degree C, respectively. As cooling led to a shift of Ca sensitivity towards higher [Ca2+] and a reduction of Cmax, the Ca sensitivity curves over this range of temperatures do not cross over as has been described for canine Purkinje fibers (Fabiato 1985). Since tension is decreased by cooling at all levels of [Ca2+] it is unlikely that changes in myofilament Ca sensitivity play a role in the large hypothermic inotropy seen in rabbit ventricular muscle. The increase in sensitivity of the myofilaments to Ca on warming from 1 to 29 degrees C might be related to the increase in force seen on rewarming from a rapid cooling contracture in intact rabbit ventricular muscle. 相似文献