全文获取类型
收费全文 | 21823篇 |
免费 | 1985篇 |
国内免费 | 5篇 |
出版年
2022年 | 177篇 |
2021年 | 348篇 |
2020年 | 165篇 |
2019年 | 271篇 |
2018年 | 254篇 |
2017年 | 277篇 |
2016年 | 467篇 |
2015年 | 764篇 |
2014年 | 920篇 |
2013年 | 1161篇 |
2012年 | 1495篇 |
2011年 | 1555篇 |
2010年 | 1014篇 |
2009年 | 841篇 |
2008年 | 1300篇 |
2007年 | 1380篇 |
2006年 | 1178篇 |
2005年 | 1160篇 |
2004年 | 1127篇 |
2003年 | 1129篇 |
2002年 | 1031篇 |
2001年 | 277篇 |
2000年 | 263篇 |
1999年 | 274篇 |
1998年 | 293篇 |
1997年 | 216篇 |
1996年 | 197篇 |
1995年 | 183篇 |
1994年 | 173篇 |
1993年 | 182篇 |
1992年 | 225篇 |
1991年 | 205篇 |
1990年 | 172篇 |
1989年 | 163篇 |
1988年 | 181篇 |
1987年 | 170篇 |
1986年 | 147篇 |
1985年 | 173篇 |
1984年 | 199篇 |
1983年 | 169篇 |
1982年 | 138篇 |
1981年 | 167篇 |
1980年 | 148篇 |
1979年 | 132篇 |
1978年 | 105篇 |
1977年 | 106篇 |
1976年 | 104篇 |
1975年 | 72篇 |
1974年 | 81篇 |
1973年 | 70篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
In vivo EMG biofeedback was found to be an effective pedagogical tool for removing unwanted left-hand tension in nine violin and viola players. Improvement occurred rapidly and persisted throughout a 5-month follow-up period. Further studies will be necessary to assess the effect of biofeedback independent of placebo effects. The brevity of the method and the magnitude of improvement warrant further investigation. 相似文献
2.
Transcriptional control, translation and function of the products of the five open reading frames of the Escherichia coli nir operon 总被引:3,自引:0,他引:3
Nerina R. Harborne Lesley Griffiths Stephen J. W. Busby Jeffrey A. Cole 《Molecular microbiology》1992,6(19):2805-2813
Five open reading frames designated nirB, nirD, nirE, nirC and cysG have been identified from the DNA sequence of the Escherichia coli nir operon. Complementation experiments established that the NirB, NirD and CysG polypeptides are essential and sufficient for NADH-dependent nitrite reductase activity (EC 1.6.6.4). A series of plasmids has been constructed in which each of the open reading frames has been fused in-phase with the beta-galactosidase gene, lacZ. Rates of beta-galactosidase synthesis during growth in different media revealed that nirB, -D, -E and -C are transcribed from the FNR-dependent promoter, p-nirB, located just upstream of the nirB gene: expression is co-ordinately repressed by oxygen and induced during anaerobic growth. Although the nirB, -D and -C open reading frames are translated into protein, no translation of nirE mRNA was detected. The cysG gene product is expressed from both p-nirB and a second, FNR-independent promoter, p-cysG, located within the nirC gene. No NADH-dependent nitrite reductase activity was detected in extracts from bacteria lacking either NirB or NirD, but a mixture of the two was as active as an extract from wild-type bacteria. Reconstitution of enzyme activity in vitro required stoichiometric quantities of NirB and NirD and was rapid and independent of the temperature during mixing. NirD remained associated with NirB during the initial stages of purification of the active enzyme, suggesting that NirD is a second structural subunit of the enzyme. 相似文献
3.
Field observations of two sympatric pitheciine species reveal that the positional repertoire of the white-faced saki, Pithecia pithecia, is dominated by leaping behaviors, whereas the bearded saki, Chiropotes satanas, is predominantly quadrupedal. Examination and comparison of the postcranial skeletal morphologies and limb proportions of these species display numerous features associated with their respective locomotor behaviors. These observations accord with associations found in other primate and mammalian groups and with predictions based on theoretical and experimental biomechanics. Preliminary observations of the skeletal morphology of Cacajao calvus demonstrate a marked similarity to that of Chiropotes. The fossil platyrrhine Cebupithecia sarmientoi displays greater similarity to Pithecia, suggesting that its positional repertoire also included significant leaping and clinging behaviors. 相似文献
4.
5.
Jo-Anne M.D. Murray Catherine Dunnett Meriel J.S. Moore-Colyer Annette C. Longland 《Animal Feed Science and Technology》2012,171(2-4):192-204
A series of in vitro experiments were conducted to assess three fibrolytic enzyme preparations as potential feed additives in equine diets. The three fibrolytic enzyme preparations were a concentrated cellulase (E1), an acid cellulase (E2) and a concentrated xylanase (E3). The enzymes were evaluated on their ability to modify the cell wall fraction of high-temperature dried lucerne (HTL) under various experimental conditions including differences in temperature, pH, incubation period, substrate levels and particle size to enable selection of the enzyme preparation most effective in the hydrolysis of lucerne. Results showed enzyme activities (as measured by reducing sugar assays) to be greatest at 50 °C, pH 5 and over an incubation period of greater than 20 h. E1 exhibited the greatest effect on total monosaccharide release from the HTL compared to E2 and E3. Moreover, dry matter (DM) and total non-starch polysaccharide (TNSP) losses were also greater in HTL treated with E1 compared to E2 and E3. Therefore, since the cell wall fraction of HTL contained substantial amounts of cellulose, the enzyme with the highest cellulase activity (Enzyme 1) was most effective in hydrolysing the cell walls of HTL. Consequently, it would appear that the application of exogenous fibrolytic enzyme preparations to forages requires the chemical characterisation of the target forage to enable selection of enzymes that are (a) most suitable to degrade the cell wall components of the candidate forage and (b) effective under field conditions. 相似文献
6.
Mandana Nikpour Dafna D Gladman Dominique Ibanez Paula J Harvey Murray B Urowitz 《Arthritis research & therapy》2010,12(3):R125
Introduction
Total cholesterol (TC) and blood pressure (BP) are likely to take a dynamic course over time in patients with systemic lupus erythematosus (SLE). This would have important implications in terms of using single-point-in-time measurements of these variables to assess coronary artery disease (CAD) risk. The objective of this study was to describe and quantify variability over time of TC and BP among patients with SLE and to determine their correlates. 相似文献7.
The eggs, larvae and pelagic juveniles ofOstracion meleagris, Lactoria fornasini andLactoria diaphana were identified from reared and field collected specimens from Hawaii, Japan, Australia and the eastern Pacific. Eggs are large and pelagic with limited chorion ornamentation and a cluster of oil droplets. At hatching, larvae are well developed, rotund, and enclosed in a dermal sac. The sac disappears and dermal plates form prior to notochord flexion. Larvae of the three species can be distinguished by their pigment patterns and development of the carapace of ossified dermal plates. Eggs of the three species could not be distinguished. The larval stage ends at a small size (< 6 mm) but the juveniles may grow to a substantial size while remaining pelagic.L. diaphana matures and spawns while pelagic in the eastern Pacific. 相似文献
8.
9.
R. Milne Murray 《BMJ (Clinical research ed.)》1887,2(1401):1020-1021
10.