全文获取类型
收费全文 | 8658篇 |
免费 | 673篇 |
国内免费 | 635篇 |
出版年
2023年 | 102篇 |
2022年 | 135篇 |
2021年 | 475篇 |
2020年 | 293篇 |
2019年 | 371篇 |
2018年 | 378篇 |
2017年 | 300篇 |
2016年 | 367篇 |
2015年 | 567篇 |
2014年 | 685篇 |
2013年 | 703篇 |
2012年 | 828篇 |
2011年 | 718篇 |
2010年 | 430篇 |
2009年 | 402篇 |
2008年 | 461篇 |
2007年 | 377篇 |
2006年 | 292篇 |
2005年 | 245篇 |
2004年 | 191篇 |
2003年 | 184篇 |
2002年 | 160篇 |
2001年 | 144篇 |
2000年 | 128篇 |
1999年 | 106篇 |
1998年 | 69篇 |
1997年 | 82篇 |
1996年 | 80篇 |
1995年 | 58篇 |
1994年 | 47篇 |
1993年 | 45篇 |
1992年 | 64篇 |
1991年 | 49篇 |
1990年 | 51篇 |
1989年 | 33篇 |
1988年 | 39篇 |
1987年 | 26篇 |
1986年 | 24篇 |
1985年 | 36篇 |
1984年 | 33篇 |
1983年 | 15篇 |
1982年 | 16篇 |
1981年 | 8篇 |
1979年 | 7篇 |
1978年 | 11篇 |
1974年 | 11篇 |
1973年 | 7篇 |
1971年 | 10篇 |
1967年 | 7篇 |
1966年 | 9篇 |
排序方式: 共有9966条查询结果,搜索用时 31 毫秒
71.
S.N. Wang P. Xu H.Z. Tang J. Meng X.L. Liu J. Huang H. Chen Y. Du H.D. Blankespoor 《Biotechnology letters》2005,26(19):1493-1496
A Pseudomonas sp. grew with nicotine optimally 3 g l–1 and at 30 °C and pH 7. Nicotine was fully degraded within 10 h. The resting cells degraded nicotine in tobacco solid waste completely within 6 h in 0.02 m sodium phosphate buffer (pH 7) at maximally 56 mg nicotine h–1 g dry cell–1. 相似文献
72.
Ján Vojtaššák Dušan Poruban Dušan Bakoš L’udovít Danihel Miroslav Korbel’ L’uboš Danišovič Daniel Böhmer Angelika Danihelová Peter Michalka Branislav Vojtaššák Milan Blaško Milan Blaško Sr. 《Biologia》2006,61(6):713-718
The use of in vitro prepared biosynthetic grafts can considerably improve the patient’s quality of life. This work reports on the use of an autologous
graft prepared from a patient’s preputial cells cultivated on biodegradable polymeric membrane. Coladerm membrane is based
on the chemically modified polyelectrolyte complex of atelocollagen and hyaluronan. The graft was used to cover a defect in
the mouth cavity base and tongue after reconstruction surgery performed at this site in the past. The presented clinical case
showed that the autologous biosynthetic graft prepared from foreskin cells can be successfully used for covering of medium-size
defects in mouth cavity base resulting in the regeneration of target mouth structures with significant improvement of patient’s
quality of life. 相似文献
73.
74.
In order to investigate the pharmacological basis of ‘Yang-invigorating’ action, the effect of oral treatment with the methanolic extract of ‘Yang-invigorating’ herbs on ATP-generation capacity was examined, using heart homogenates prepared from herb-pretreated mice. Tonifying (i.e., health-promoting) herbs of other functional categories were also included for comparison. The results indicated that ‘Yang-invigorating’ Chinese tonifying herbs could invariably enhance myocardial ATP-generation capacity, with the extent of stimulation varying among the herbs. In contrast, ‘Yin-nourishing’ herbs either did not stimulate or even decreased myocardial ATP-generation capacity. While ‘Qi-invigorating’ herbs produced variable effects on myocardial ATP-generation capacity, most of the ‘blood-enriching’ herbs did not cause any significant changes. The results obtained from studies using myocardial mitochondrial fractions isolated from herb-pretreated mice suggest that ‘Yang-invigorating’ herbs might speed up ATP generation by increasing mitochondrial electron transport. The ensemble of results has provided evidence for the first time to support the pharmacological basis of ‘Yang invigoration’ in Chinese medicine. 相似文献
75.
Hua Zou Guo-Cheng Du Wen-Quan Ruan Jian Chen 《World journal of microbiology & biotechnology》2006,22(7):701-706
Summary The effects of nitrate on phosphorus release and uptake in a sequencing batch reactor for biological phosphorus removal was
investigated. The addition of nitrate decreased phosphorus release in the anaerobic stage. The synthesis of poly(hydroxyalkanoates)
was decreased with the presence of nitrate, possibly due to the competitive utilization of the carbon source by PHA synthesis
and denitrification of nitrate. Instead of oxygen, nitrate could be used as an electron acceptor for phosphorus removal. However,
the simultaneous addition of nitrate and acetate greatly reduced the phosphorus removal rate. Phosphate and nitrate could
be removed simultaneously with nitrate as the electron acceptor, and the continuous and steady feeding of nitrate was beneficial
to phosphate removal. 相似文献
76.
Ischemia impairs the association between connexin 43 and M3 subtype of acetylcholine muscarinic receptor (M3-mAChR) in ventricular myocytes. 总被引:3,自引:0,他引:3
Peng Yue Yong Zhang Zhimin Du Jing Xiao Zhenwei Pan Ning Wang Haiyan Yu Wencai Ma Hong Qin Wen-Hui Wang Dao-Hong Lin Baofeng Yang 《Cellular physiology and biochemistry》2006,17(3-4):129-136
We used Western blot analysis to examine the expression of connexin 43 and M2/M3 acetylcholine muscarinic receptors (mAChR) and their interaction in ventricular myocytes from control and the ischemic heart. We confirmed that the connexin 43 and M2/ M3-mAChR were expressed in ventricular myocytes. Moreover, we showed that M3-mAChR was expressed in non-glycosylated (72 kDa) and glycosylated forms (115 kDa). Immunostaining showed that connexin 43 is closely associated with M3-mAChR in parts of cell membranes of myocytes. Immunoprecipitation of lysate of cardiac myocytes with M2/M3-mAChR antibody pulled down a 44 kDa protein recognized by connexin 43 antibody. Ischemia increased the expression of M3-mAChR in myocytes. The ischemiainduced increase in the M3-mAChR expression was specific because ischemia did not affect the expression of M1, M2, M4 and M5- mAChR in the heart. On the other hand, ischemia decreased the expression of connexin 43 in myocardium. We also examined the effect of ischemia on the interaction between M2/M3-mAChR and connexin 43. Ischemia suppressed the association of M3-mAChR with connexin 43 but did not affect the association of connexin 43 with M2-mAChR. Administration of choline before ischemia not only partially restored the expression of connexin 43 but also attenuated the ischemia-induced suppression of the association between connexin 43 and M3-mAChR. We conclude that connexin 43 interacts with M2/M3-mAChR and that ischemia specifically impairs the association between M3-mAChR and connexin 43. 相似文献
77.
Importance of assemblage‐level thinning: A field experiment in an alpine meadow on the Tibet plateau
Question: Which fraction of the decrease in species richness under fertilization can be explained by assemblage‐level thinning? Location: An alpine meadow on the eastern Tibet plateau. Methods: 60‐m2 plots were randomly assigned to a control or one of four levels of ammonium phosphate fertilizer. Treatments were repeated for three years. The effect of as semblage‐level thinning was decided based on similarity in quadrats within and between fertilizing levels, bootstrap simulation based on random thinning of the high density (low production, low fertility) quadrats and correlation of species’ biomass in low fertility and high fertility. Results: Fertilization increased production, reduced species richness and reduced density of individuals. Heavily fertilized quadrats are more similar in species composition in 2000 but less similar in 2001 and 2002. Rarefaction showed that a decrease in density can account for 32.3‐42.9% decrease of species richness, but the simulated species richness is always significantly higher than the observed one. When production and species richness are similar at two levels of fertilization, species biomass in the higher fertility treatment is positively correlated with biomass at lower fertility. When the two fertilizer levels differed in production and species richness, there was no evidence of correlation in species biomass, suggesting that assemblage level thinning cannot explain all the loss of species. Conclusion: Although a decrease in density could explain much of the decrease (up to 42.9%) in species richness when this alpine meadow was fertilized, other important mechanisms such as interspecific competition cannot be ignored. Future studies should investigate the effect of assemblage level thinning on species diversity, and search for mechanisms responsible for a decrease in diversity. 相似文献
78.
Li Wang Wei Du Dehua Liu Lilin Li Ningmei Dai 《Journal of Molecular Catalysis .B, Enzymatic》2006,43(1-4):29-32
Lipase-catalyzed alcoholysis of soybean oil deodorizer distillate (SODD) for biodiesel production was studied. During this system both free fatty acids and glycerides could be converted to biodiesel simultaneously. tert-Butanol has been adopted as the reaction medium, in which both the negative effects caused by excessive methanol and by-product glycerol could be eliminated completely. There was no obvious loss in lipase activity even after being repeatedly used for 120 cycles. Fine-pored silica gel and 3 Å molecular were found to be effective to control by-product water concentration and much higher biodiesel yield could be achieved with those adsorbents present in the reaction system. The highest biodiesel yield of 97% could be achieved with 3 Å molecular sieve as the adsorbent. 相似文献
79.
Yunfei Li Haitao Liu Caiyong Lai Xinghua Du Zexuan Su Shuangquan Gao 《Cell and tissue research》2013,354(2):533-541
We investigate the role of the Lin28/let-7a/c-Myc pathway in non-muscle invasive bladder cancer (NMIBC). Using RT-PCR, western blot and immunohistochemistry techniques, the levels of pre-let-7a, let-7a, Lin28 and c-Myc RNA and/or proteins were determined in samples of normal bladder tissue and bladder cancer. Expression of pre-let-7a was found to be negatively correlated with the pathological grade of bladder cancer, while let-7a showed a positive correlation with bladder cancer pathological grade. Expression of Lin28 RNA and protein was not significantly different between normal bladder tissue and low-grade transitional cell carcinoma of bladder (TCC) but the expression levels in high-grade TCC were remarkably increased. Expression of c-Myc RNA and protein was significantly higher in bladder cancer samples in comparison to normal bladder tissue without correlation with cancer differentiation. Expression of all the above RNAs and proteins showed no significant difference in Ta and T1 stages. The Lin28/let-7a/c-Myc pathway plays an important role in NMIBC. In particular, expression levels of let-7a correlate with the degree of cancer differentiation but not cancer stage. 相似文献
80.
Hydrogen sulfide donor sodium hydrosulfide-improved heat tolerance in maize and involvement of proline 总被引:2,自引:0,他引:2
Hydrogen sulfide (H2S) has long been considered as a phytotoxin, but nowadays as a cell signal molecule involved in growth, development, and the acquisition of stress tolerance in higher plants. In the present study, hydrogen sulfide donor, sodium hydrosulfide (NaHS), pretreatment markedly improved germination percentage of seeds and survival percentage of seedlings of maize under heat stress, and alleviated an increase in electrolyte leakage of roots, a decrease in tissue vitality and an accumulation of malondialdehyde (MDA) in coleoptiles of maize seedlings. In addition, pretreatment of NaHS could improve the activity of Δ1-pyrroline-5-carboxylate synthetase (P5CS) and lower proline dehydrogenase (ProDH) activity, which in turn induced accumulation of endogenous proline in maize seedlings. Also, application of proline could enhance endogenous proline content, followed by mitigated accumulation of MDA and increased survival percentage of maize seedlings under heat stress. These results suggest that sodium hydrosulfide pretreatment could improve heat tolerance of maize and the acquisition of this heat tolerance may be involved in proline. 相似文献