全文获取类型
收费全文 | 759篇 |
免费 | 47篇 |
出版年
2023年 | 2篇 |
2022年 | 6篇 |
2021年 | 20篇 |
2020年 | 13篇 |
2019年 | 13篇 |
2018年 | 10篇 |
2017年 | 27篇 |
2016年 | 23篇 |
2015年 | 29篇 |
2014年 | 34篇 |
2013年 | 49篇 |
2012年 | 67篇 |
2011年 | 67篇 |
2010年 | 43篇 |
2009年 | 33篇 |
2008年 | 49篇 |
2007年 | 35篇 |
2006年 | 44篇 |
2005年 | 38篇 |
2004年 | 23篇 |
2003年 | 27篇 |
2002年 | 29篇 |
2001年 | 16篇 |
2000年 | 18篇 |
1999年 | 9篇 |
1998年 | 4篇 |
1997年 | 2篇 |
1996年 | 3篇 |
1995年 | 9篇 |
1994年 | 3篇 |
1993年 | 2篇 |
1991年 | 2篇 |
1990年 | 3篇 |
1988年 | 4篇 |
1987年 | 7篇 |
1986年 | 3篇 |
1985年 | 5篇 |
1984年 | 7篇 |
1983年 | 2篇 |
1982年 | 2篇 |
1979年 | 5篇 |
1978年 | 2篇 |
1977年 | 4篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1972年 | 3篇 |
1970年 | 1篇 |
1969年 | 1篇 |
1964年 | 1篇 |
1958年 | 1篇 |
排序方式: 共有806条查询结果,搜索用时 15 毫秒
1.
Summary Two varieties of tomato (Pusa Rubi and Selection 120) positively responded to algal inoculation in terms of the yield of fruits and shoots, but there was no significant effect on the vitamin C content of the fruits. A combined application of urea and algae was more effective than the application of urea alone. 相似文献
2.
The isolated blood-perfused lung preparation is widely used to visualize and define signaling in single microvessels. By coupling this preparation with real time imaging, it becomes feasible to determine permeability changes in individual pulmonary microvessels. Herein we describe steps to isolate rat lungs and perfuse them with autologous blood. Then, we outline steps to infuse fluorophores or agents via a microcatheter into a small lung region. Using these procedures described, we determined permeability increases in rat lung microvessels in response to infusions of bacterial lipopolysaccharide. The data revealed that lipopolysaccharide increased fluid leak across both venular and capillary microvessel segments. Thus, this method makes it possible to compare permeability responses among vascular segments and thus, define any heterogeneity in the response. While commonly used methods to define lung permeability require postprocessing of lung tissue samples, the use of real time imaging obviates this requirement as evident from the present method. Thus, the isolated lung preparation combined with real time imaging offers several advantages over traditional methods to determine lung microvascular permeability, yet is a straightforward method to develop and implement. 相似文献
3.
High level of divergence of male-reproductive-tract proteins, between Drosophila melanogaster and its sibling species, D. simulans 总被引:1,自引:0,他引:1
We compared male-reproductive-tract polypeptides of Drosophila melanogaster
and D. simulans by using two-dimensional gel electrophoresis. Approximately
64% of male-reproductive-tract polypeptides were identical between two
randomly chosen isofemale lines from these two species, compared with 83%
identity for third-instar imaginal wing-disc polypeptides. Qualitatively
similar differences were found between reproductive tracts and imaginal
discs when D. sechellia was compared with D. melanogaster and with D.
simulans. When genic polymorphism was taken into account, approximately 10%
of male- reproductive-tract polypeptides were apparently fixed for
different alleles between D. melanogaster and D. simulans; this proportion
is the same as that found for soluble enzymes by one-dimensional gel
electrophoresis. Strikingly, approximately 20% of male-reproductive- tract
polypeptides of either D. melanogaster or D. simulans had no detectable
homologue in the other species. We propose that proteins of the Drosophila
male reproductive tract may have diverged more extensively between species
than have other types of proteins and that much of this divergence may
involve large changes in levels of polypeptide expression.
相似文献
4.
A postprandial increase in ammonia nitrogen excretion and oxygen consumption rates was observed in juvenile pike fed a natural diet or an artificial dry diet. Specific growth rate of natural diet fed pike (2.4%) was lower than that of pike fed the artificial diet (3.1%). Fifty per cent of ingesta was evacuated within 5–6 h in pike of 25 mg body weight and 9–10 h in those weighing 150mg. Daily nitrogen excretion rates were related to body weight. Respiratory quotient and energy retention efficiency were affected by the nature of the diet ingested by pike. Parameters of the energy balance (losses, retention, increment due to feeding) were related to energy intake. 相似文献
5.
Patterns of oxygen consumption, ammonia and urea excretion were monitored during late embryogenesis, i.e. 5 days before mass hatching and 12 days during the free-swimming stage of whitefish larvae, Coregonus lavaretus. Oxygen consumption increased from 1.31 to 2.53 mgO2 h−1 × 103 eggs−1 at hatching. Fasted, free-swimming larvae showed increasing oxygen consumption to the tenth day after hatching when it reached 5.52 mgO2 h−1 × 103 larvae−1 . Ammonia and urea excretion increased during pre-hatching period from 52.1 to 163.2 and 26.8 to 51.4 μgh−1 × 103 eggs−1 , respectively. The nitrogen excretion rate increased between the sixth and tenth day of fasting, i.e. for ammonia from 117.7 to 160.9 and for urea from 35.8 to 52.5 μg h−1 × 103 larvae−1 . Cumulative data on nitrogen and energy metabolism indicated that during late embryogenesis, and up to the fifth day after hatching, protein dominated in the energy expenditure. During the free swimming stage, the ratio of fat to protein in energy expenditure rose from 0.86 to 1.99. Combined data for several fish species indicated high dependance of oxygen uptake during the hatching period on egg size and temperature. 相似文献
6.
Identification of a new V kappa gene family that is highly expressed in hybridomas from an autoimmune mouse strain 总被引:2,自引:0,他引:2
R Shefner R Mayer A Kaushik P D'Eustachio C Bona B Diamond 《Journal of immunology (Baltimore, Md. : 1950)》1990,145(5):1609-1614
We have identified a new murine V kappa family that contains five to seven members, one member of which encodes the L chain V region of an anti-dsDNA antibody produced by a BALB/c hybridoma, C8.5. The cloned C8.5 V kappa gene exhibits highest homology with a human V kappa gene that was cloned from a nonproductive rearrangement but has never been seen in an expressed repertoire. Because this family was first identified in an autoantibody, we studied its expression in an autoimmune mouse strain. This V kappa family is expressed in 20% of hybridomas from NZB mice. 相似文献
7.
L. S. Kaushik D. P. Singh R. S. Paroda 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1984,68(6):487-491
Summary The data from an experiment in cotton consisting of three testers and 12 lines selected deliberately have been analysed. The investigation showed higher specific combining ability variance for yield of seed cotton and number of bolls, indicating the predominance of non-additive gene action. Of parental lines, H777 was found to possess high g.c.a. effects for seed cotton yield, number of bolls and number of sympodes. Parent H842 contributed only for boll weight, whereas H655 was good general combiner for number of monopodes. There appeared to be better chances for increasing the yield by exploiting hybrid vigour for the number of bolls and boll weight. The presence of marked non-additive gene effects, in addition to additive gene effects, indicated the need for exploiting both the fixable and non-fixable components of genetic variance for increasing productivity in cotton. 相似文献
8.
RS Fisher 《The Journal of general physiology》1977,69(5):571-604
When the outer surface of short-circuited frog skin was penetrated with microelectrodes, stable negative potentials that averaged near -100 mV were recorded consistently, confirming the results of Nagel (W. Nagel. 1975. Abstracts of the 5th International Biophysics Congress, Copenhagen. P-147.). The appearance of these stable potentials, V(O), concurrent with the observations that (a) a high resistance outer barrier R(O) accounting for approximately 75 percent or more of the transcellular resistance of control skins had been penetrated and that (b) 10(-5) M amiloride and reduced [Na] outside caused the values of V(O) to increase towards means value near -130 mV while the values of percent R(O) increased to more than 90 percent. It was of relationships were the same as the values of E(1) observed in studies of the current-voltage relationships were the same as the values of E’(1) defined as the values of voltage at the inner barrier when the V(O) of the outer barrier was reduced to zero by voltage clamping of the skins. Accordingly, these data are interpreted to mean that the values of E(1), approximately 130 mV, represent the E(Na) of the sodium pump at the inner barrier. 2,4-DNP was observed to decrease the values of transepithelial voltage less than E(1) the V(O) was negative. These data can be interpreted with a simple electrical equivalent circuit of the active sodium transport pathway of the frog skin that includes the idea that the outer membrane behaves as an electrical rectifier for ion transport. 相似文献
9.
A simple system for the Collection of Leaf-Derived Faecal Pellets of Aquatic Invertebrates 总被引:1,自引:1,他引:0
Animals and food (leaves) are confined at a desired temperature in a feeding chamber in the upper portion of the water column of a collector system. Egested material collects in water at 0°C also eliminates coprophagy and physical damage to the pellets. 相似文献
10.
Preliminary observations on nitrogen transport during summer in a small spring-fed Ontario stream 总被引:7,自引:4,他引:3
Nitrogen transport in a 2 km-long, spring-fed stream was studied during the summer months by analyzing weekly water samples from four stations. The water at the spring had a consistently high level of nitrate-N ranging from about 7 mg/l in late spring to about 3 mg/l in early fall. However, over the length of the stream, 60% (about 97 kg) of the incoming nitrate-N is lost from the water during the summer period. The loss, which does not appear to be attributable to the uptake by aquatic macrophytes or to immobilization, is thought to result from denitrification. 相似文献