全文获取类型
收费全文 | 17018篇 |
免费 | 1528篇 |
国内免费 | 1114篇 |
出版年
2023年 | 153篇 |
2022年 | 215篇 |
2021年 | 551篇 |
2020年 | 455篇 |
2019年 | 517篇 |
2018年 | 526篇 |
2017年 | 453篇 |
2016年 | 580篇 |
2015年 | 901篇 |
2014年 | 1021篇 |
2013年 | 1217篇 |
2012年 | 1402篇 |
2011年 | 1247篇 |
2010年 | 823篇 |
2009年 | 711篇 |
2008年 | 921篇 |
2007年 | 874篇 |
2006年 | 755篇 |
2005年 | 725篇 |
2004年 | 643篇 |
2003年 | 635篇 |
2002年 | 527篇 |
2001年 | 423篇 |
2000年 | 399篇 |
1999年 | 349篇 |
1998年 | 194篇 |
1997年 | 125篇 |
1996年 | 96篇 |
1995年 | 81篇 |
1994年 | 109篇 |
1993年 | 72篇 |
1992年 | 179篇 |
1991年 | 160篇 |
1990年 | 138篇 |
1989年 | 155篇 |
1988年 | 126篇 |
1987年 | 112篇 |
1986年 | 109篇 |
1985年 | 106篇 |
1984年 | 70篇 |
1983年 | 75篇 |
1982年 | 47篇 |
1979年 | 52篇 |
1977年 | 75篇 |
1976年 | 47篇 |
1975年 | 43篇 |
1974年 | 56篇 |
1973年 | 42篇 |
1971年 | 40篇 |
1969年 | 40篇 |
排序方式: 共有10000条查询结果,搜索用时 109 毫秒
21.
22.
D Di Berardino M Ronne I Burguete M B Lioi L Taibi D Matassino 《The Journal of heredity》1987,78(4):225-230
R-banded prometaphase karyotypes of the goat are presented using both fluorescent and light staining techniques. A model for the standardization of the R-banded prometaphase goat karyotype is suggested. 相似文献
23.
24.
25.
Flavonoids: old and new aspects of a class of natural therapeutic drugs. 总被引:25,自引:0,他引:25
Flavonoids are natural products widely distributed in the vegetable kingdom and currently consumed in large amounts in the daily diet. Flavonoids are capable of modulating the activity of enzymes and affect the behaviour of many cell systems, suggesting that the compounds may possess significant antihepatotoxic, antiallergic, anti-inflammatory, antiosteoporotic and even antitumor activities. This review summarizes available data on these beneficial effects of flavonoids. 相似文献
26.
We have tested whether increased Ca++ and Mg++ concentrations have an effect on transepithelial voltage (PDte) and transepithelial resistance (Rte) in isolated perfused cortical thick ascending limbs (cTAL) of rabbit kidney. The divalent cations added at 2.5, 5.0 and 10.0 mmol.l-1 to the lumen or peritubular bath perfusate led to a concentration-dependent increase in Rte. The maximal response in Rte was observed between 5 and 10 mmol.l-1. No significant change in active transepithelial potential difference (PDte) was observed. The increase in Rte still occurred when the transcellular current was reduced by Ba++ (3 mmol.l-1) added to the lumen perfusate. This suggests that the increase in Rte caused by Ca++ and Mg++ is due to a modification of the paracellular shunt pathway. In the absence of active transport, i.e. when furosemide (5.10(-5) mol.l-1) was added to the lumen perfusate. Ca++ and Mg++ reduced the transepithelial diffusion potential generated by a NaCl gradient established across the epithelium, and thus produced a reduction of the relative permeability for Na+ over Cl- (PNa+/PCl-) of the paracellular shunt pathway. This indicates that divalent cations increase Rte by reducing the sodium permeability of the tight junctions. The observed Ca++ and Mg++ induced reduction of the sodium permeability of the paracellular pathway corresponds to a decrease in net Na+ reabsorption by 5-10%. Since it has been demonstrated that peptide hormones such as parathyrin (PTH) modulate divalent cation and NaCl reabsorptions, in a second series of experiments we tested the effects of PTH (2-20 USP.l-1) and dbcAMP (10(-3) mol.l-1) on PDte and Rte of isolated perfused cTAL segments of rabbit nephron. Neither Rte nor PDte were affected by PTH or dbcAMP. 相似文献
27.
A silver-stainable chromatid core is visualized under the light microscope on human leukocyte chromosomes by treating fixed chromosomes with 2M NaCl.An aminoacid which is not part of histone composition, 3H-tryptophan, is used to label the synthesis and location of non-histone proteins and to study the effect on these proteins of treatment with 2M NaCl and 0.2N HCl to visualize the core. 2M NaCl is shown to remove from nuclei and chromosomes an appreciable fraction of acid proteins, as well as all those synthesized during the two hours preceding the metaphase. 3H-Try labelling seems to preferentially affect only one chromatid per chromosome. The silver-stainable halocs appearing around numerous nuclei after treatment with 2M NaCl and 0.2N HCl are found to be labelled by 3H-Try and not by 3H-TdR. 相似文献
28.
Z. Flagella R. G. Campanile M. C. Stoppelli A. De Caro N. Di Fonzo 《Physiologia plantarum》1998,104(4):753-759
The quantum yield of photosynthetic electron transport (ΦPSII), evaluated by means of chlorophyll (Chl) fluorescence analysis, has proven to be a useful screening test for drought tolerance in durum wheat (Triticum durum Desf.). To explore the potential of this parameter further in detecting drought-tolerant genotypes, three cereal species were studied; ΦPSII measurements were carried out under two different gas mixtures, at three points of the induction curve (to obtain the maximal ΦPSII and both the transient and steady-state actual ΦPSII), and at three different water stress levels (moderate, severe and drastic). The species investigated were durum and bread wheat (Triticum aestivum L.) and barley (Hordeum vulgare L.); two cultivars per species, characterized by different levels of drought tolerance, were tested. The two gas mixtures used were normal air (21% O2, 0.035% CO2 in N2) to monitor the whole photosynthetic process under physiological conditions, and CO2 enriched-low O2 air (1% O2, 5% CO2 in N2) to monitor ΦPSII reduction under stress mainly related to Calvin cycle activity. When ΦPSII related to both assimilatory and non-assimilatory metabolism was evaluated, the cultivar differences observed under normal Air were more representative of the agronomic performance upon drought stress than under high CO2-low O2 air. Maximal ΦPSII showed no difference among either cultivars, gas mixtures or stress levels, the efficiency of excitation capture being highly resistant to drought. The ΦPSII evaluated during the transient yielded predictable values in respect of drought tolerance for durum wheat and barley cultivars, highlighting the key role of regulatory processes such as the Mehler peroxidase reaction and possibly also cyclic electron transport, in preventing overreduction under stress. The results clearly show that when Chl fluorescence analysis is used as a parameter in plant breeding, different experimental conditions should be used depending on the physiological mechanism that is bred or selected for. 相似文献
29.
A peptide, eluted with cytochrome c, called 'big' somatostatin, is the only somatostatin-like immunoreactivity present in the peripheral plasma of the duck. The metabolic action of partially purified fractions of 'big' somatostatin was investigated on glucagon-stimulated lipolysis in chicken adipocytes. Significant inhibition of glycerol release (an index of lipolysis) induced by physiological concentrations of glucagon was observed with physiological concentrations of 'big' somatostatin; the percentage of inhibition was dose-dependent. 相似文献
30.
P Fantazzini L Lendinara F Novello E Brosio A Di Nola 《Biochimica et biophysica acta》1984,803(4):250-253
We report the proton spin-lattice relaxation times (T1) of rat liver samples taken at different times after partial hepatectomy. The T1 values obtained are compared with those of liver samples from sham-operated rats and of liver samples from rats that had not undergone any surgical treatment. The results show that surgical stress significantly influences the T1 values of sham-operated rats both in their absolute value and in their dependence on the time after the operation, while it induces only a modest early increase of the water content. Possible effects of liver regeneration on 1H-T1 are almost completely concealed by the changes due to the surgical operation. These results emphasize the importance of the choice of a suitable control for T1 measurements in biological systems. 相似文献