全文获取类型
收费全文 | 292537篇 |
免费 | 34348篇 |
国内免费 | 148篇 |
出版年
2018年 | 2408篇 |
2016年 | 3090篇 |
2015年 | 4050篇 |
2014年 | 4926篇 |
2013年 | 6760篇 |
2012年 | 7729篇 |
2011年 | 7942篇 |
2010年 | 5219篇 |
2009年 | 5048篇 |
2008年 | 7166篇 |
2007年 | 7351篇 |
2006年 | 7223篇 |
2005年 | 6943篇 |
2004年 | 6802篇 |
2003年 | 6636篇 |
2002年 | 6476篇 |
2001年 | 17256篇 |
2000年 | 17440篇 |
1999年 | 13264篇 |
1998年 | 3767篇 |
1997年 | 4033篇 |
1996年 | 3739篇 |
1995年 | 3490篇 |
1994年 | 3466篇 |
1993年 | 3546篇 |
1992年 | 10396篇 |
1991年 | 10329篇 |
1990年 | 9810篇 |
1989年 | 9643篇 |
1988年 | 8995篇 |
1987年 | 8360篇 |
1986年 | 7563篇 |
1985年 | 7412篇 |
1984年 | 5827篇 |
1983年 | 5075篇 |
1982年 | 3619篇 |
1981年 | 3183篇 |
1980年 | 3037篇 |
1979年 | 5355篇 |
1978年 | 4123篇 |
1977年 | 3756篇 |
1976年 | 3297篇 |
1975年 | 3778篇 |
1974年 | 3948篇 |
1973年 | 3897篇 |
1972年 | 3425篇 |
1971年 | 3187篇 |
1970年 | 2824篇 |
1969年 | 2743篇 |
1968年 | 2412篇 |
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
991.
The light organ symbiont Vibrio fischeri possesses two distinct secreted ADP-ribosyltransferases. 下载免费PDF全文
We have previously described the purification, cloning, and initial characterization of a secreted ADP-ribosyltransferase, halovibrin (gene designation hvn), from the luminescent light organ symbiont Vibrio fischeri. This report describes a strategy for overexpression of halovibrin, the production and refinement of antihalo-vibrin antisera, and the molecular biological construction of a V. fischeri halovibrin null strain. Biochemical analysis of this mutant revealed that V. fischeri hvn null still possessed ADP-ribosyltransferase activity and that this activity is immunologically, genetically, and structurally distinct from the previously described enzyme. This unusual finding, of two ADP-ribosyltransferase enzymes produced by a microorganism, is complemented by the details of the purification to apparent homogeneity and in vitro regulation of this new protein, halovibrin-beta. 相似文献
992.
993.
S. Z. Whetzel Y. H. Shih L. M. Georgic H. C. Akunne T. A. Pugsley 《Journal of neurochemistry》1997,69(6):2363-2368
Abstract: The dopamine (DA) D3 receptor antagonist PD 58491 {3-[4-[1-[4-[2-[4-(3-diethylaminopropoxy)phenyl]-benzoimidazol-1-yl-butyl]-1 H -benzoimidazol-2-yl]-phenoxy]propyl]diethylamine} bound with high affinity and selectivity to recombinant human DA D3 versus D2L and D4.2 receptors transfected into Chinese hamster ovary cells: K i values of 19.5 n M versus 2,362 and >3,000 n M , respectively. In contrast, the putative DA D3 receptor antagonist (+)-AJ76 displayed low affinity and selectivity for D3 versus D2L and D4.2 receptors (91 n M vs. 253 and 193 n M , respectively). In vitro, PD 58491 (1 n M −1µ M ) exhibited D3 receptor antagonist activity, reversing the quinpirole (10 n M )-induced stimulation of [3 H]thymidine uptake in D3 CHOpro-5 cells, but did not have any significant intrinsic activity by itself in this assay. PD 58491 did not decrease the γ-butyrolactone-induced increase in DA synthesis ( l -3,4-dihydroxyphenylalanine accumulation) in rat striatum, indicating that the compound possessed no in vivo DA D2 /D3 receptor agonist action at DA autoreceptors. PD 58491 (3–30 mg/kg, i.p.) generally did not alter DA or serotonin synthesis in either the striatum or mesolimbic region of rat brain. The D3 -preferring agonist PD 128907 decreased DA synthesis in striatum and mesolimbic regions, and this effect was attenuated by pretreatment with PD 58491. These findings support the hypothesis that DA D3 autoreceptors may in part modulate the synthesis and release of DA in striatum and mesolimbic regions. 相似文献
994.
The effects of four xanthine derivatives, caffeine, caffeine benzoate, theophylline, and bromtheophylline, on sodium channels
in internally perfused rat dorsal root ganglion neurons were studied under voltage-clamp and whole-cell patch-clamp conditions.
Reversible acceleration, enhancement of the amplitude of sodium currents, and shifts of the current-voltage relation (plotted
for their maxima), as well as of the steady-state inactivation curve toward more negative potentials, were observed at external
applications of the above substances in the concentrations of 0.2–4.0 mM. Under long exposures, inactivation of sodium currents
became slower in a part of the cells. Yet, when the exposure to 4 mM or higher concentrations was longer than 10 min, a rise
in the passive conductance was obvious, and functional state of the cells became worse. Blocking effects of the xanthine derivatives
on transient or delayed potassium currents were not observed. Thus, agonistic action of xanthines on sodium channels has been
demonstrated, and it is supposed that a considerable component of their pharmacological effects is provided by the action
on Na+/Ca2+ exchange. 相似文献
995.
The recolonization of the Krakatau islands by termites (Isoptera), and their biogeographical origins 总被引:1,自引:0,他引:1
F.J. GATHORNE-HARDY D. T.JONES N. A. MAWDSLEY 《Biological journal of the Linnean Society. Linnean Society of London》2000,71(2):251-267
The termite assemblages of the Krakatau islands and five sites in Sumatra and Java were investigated, using a standardized transect sampling method. Five species were found on the Krakatau islands that have not been collected there before. The total number of termites recorded on the islands since the 1883 volcanic eruption is now twelve species, all of which are wood feeders. No termites nesting in or feeding on the soil were found on the Krakataus, suggesting that rafting in wood is the primary method by which the termites recolonized the islands. 相似文献
996.
997.
A M Belles T J Montville B P Wasserman 《Journal of industrial microbiology & biotechnology》2000,24(1):71-74
Alcohol-extractable, hydrophobic zein proteins contaminate starch granule surfaces and can be removed by enzymatic digestion
with thermolysin. The goal of this research was to find practical alternatives to thermolysin that might be used during the
corn wet-milling process. All of the commercial thermostable alkaline proteases studied (SP 709, Neutrase, and Spezyme FAN)
removed the zein proteins from various types of cornstarch, as demonstrated by the lack of protein bands below 30 kDa under
the reducing conditions of SDS-PAGE gel. Each enzyme removed the zein proteins as effectively as thermolysin removed them.
However, the removal of the zein protein did not reduce the quantity of free fatty acids associated with the starch. Journal of Industrial Microbiology & Biotechnology (2000) 24, 71–74.
Received 27 May 1999/ Accepted in revised form 01 October 1999 相似文献
998.
S F Silverton O A Adebanjo B S Moonga E M Awumey T Malinski M Zaidi 《Biochemical and biophysical research communications》1999,259(1):73-77
Nitric oxide (NO) triggers marked osteoclast retraction which closely resembles that due to Ca2+. The effect of Ca2+ has been attributed to a stimulated release of NO. Here, we show for the first time, by direct measurement with a microsensor, that osteoclasts do indeed produce NO and that this production is enhanced by a high Ca2+. We also show that the Ca2+ ionophore, A23187, mimics the latter. Furthermore, osteoclasts on dentine produce more NO than osteoclasts on glass and NO release from dentine-plated osteoclasts is much less sensitive to stimulation by Ca2+. Finally, the microsomal Ca2+ store-depleting agent, thapsigargin, attenuates NO release only from osteoclasts on glass, suggesting that stored Ca2+ has the dominant effect in modulating NO release from non-resorbing cells. NO is a powerful inhibitor of bone resorption: a direct demonstration of its production is therefore strong evidence for a role in modulating osteoclast function. 相似文献
999.
Isolation of a VP1 homologue from wheat and analysis of its expression in embryos of dormant and non-dormant cultivars. 总被引:7,自引:0,他引:7
A VP (Viviparous) 1 homologous gene has been cloned from wheat (Triticum aestivumL.). Its expression level was examined in the mature embryos of dormant and non-dormant cultivars. The level of expression was positively correlated with the level of seed dormancy and embryo sensitivity to abscisic acid (ABA). 相似文献
1000.
The purpose of this investigation was to determine whether plasma glucose kinetics and substrate oxidation during exercise are dependent on the phase of the menstrual cycle. Once during the follicular (F) and luteal (L) phases, moderately trained subjects [peak O(2) uptake (V(O(2))) = 48.2 +/- 1.1 ml. min(-1). kg(-1); n = 6] cycled for 25 min at approximately 70% of the V(O(2)) at their respective lactate threshold (70%LT), followed immediately by 25 min at 90%LT. Rates of plasma glucose appearance (R(a)) and disappearance (R(d)) were determined with a primed constant infusion of [6,6-(2)H]glucose, and total carbohydrate (CHO) and fat oxidation were determined with indirect calorimetry. At rest and during exercise at 70%LT, there were no differences in glucose R(a) or R(d) between phases. CHO and fat oxidation were not different between phases at 70%LT. At 90%LT, glucose R(a) (28.8 +/- 4.8 vs. 33.7 +/- 4.5 micromol. min(-1). kg(-1); P < 0.05) and R(d) (28.4 +/- 4.8 vs. 34.0 +/- 4.1 micromol. min(-1). kg(-1); P < 0.05) were lower during the L phase. In addition, at 90%LT, CHO oxidation was lower during the L compared with the F phase (82.0 +/- 12.3 vs. 93.8 +/- 9.7 micromol. min(-1) .kg(-1); P < 0.05). Conversely, total fat oxidation was greater during the L phase at 90%LT (7.46 +/- 1.01 vs. 6.05 +/- 0.89 micromol. min(-1). kg(-1); P < 0.05). Plasma lactate concentration was also lower during the L phase at 90%LT concentrations (2.48 +/- 0.41 vs. 3.08 +/- 0.39 mmol/l; P < 0.05). The lower CHO utilization during the L phase was associated with an elevated resting estradiol (P < 0.05). These results indicate that plasma glucose kinetics and CHO oxidation during moderate-intensity exercise are lower during the L compared with the F phase in women. These differences may have been due to differences in circulating estradiol. 相似文献