全文获取类型
收费全文 | 9168篇 |
免费 | 608篇 |
国内免费 | 616篇 |
专业分类
10392篇 |
出版年
2024年 | 23篇 |
2023年 | 98篇 |
2022年 | 240篇 |
2021年 | 436篇 |
2020年 | 302篇 |
2019年 | 372篇 |
2018年 | 361篇 |
2017年 | 271篇 |
2016年 | 345篇 |
2015年 | 558篇 |
2014年 | 658篇 |
2013年 | 717篇 |
2012年 | 802篇 |
2011年 | 757篇 |
2010年 | 441篇 |
2009年 | 413篇 |
2008年 | 468篇 |
2007年 | 394篇 |
2006年 | 361篇 |
2005年 | 303篇 |
2004年 | 258篇 |
2003年 | 233篇 |
2002年 | 185篇 |
2001年 | 174篇 |
2000年 | 151篇 |
1999年 | 141篇 |
1998年 | 104篇 |
1997年 | 95篇 |
1996年 | 83篇 |
1995年 | 72篇 |
1994年 | 82篇 |
1993年 | 66篇 |
1992年 | 71篇 |
1991年 | 66篇 |
1990年 | 66篇 |
1989年 | 51篇 |
1988年 | 32篇 |
1987年 | 35篇 |
1986年 | 22篇 |
1985年 | 27篇 |
1984年 | 10篇 |
1983年 | 16篇 |
1982年 | 8篇 |
1981年 | 4篇 |
1980年 | 6篇 |
1979年 | 6篇 |
1978年 | 2篇 |
1977年 | 2篇 |
1976年 | 2篇 |
1972年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
A versatile strategy has been developed for selectively and sequentially isolating targets in a liquid-phase affinity separation environment. The strategy uses a recently developed approach for joining together molecules in linkages that are defined by the complementary pairing of oligonucleotides conjugated to the different molecules [Niemeyer, C. M., Sano, T., Smith, C. L., and Cantor, C. R. (1994) Nucleic Acids Res. 22, 5530-9]. In the work presented here, streptavidin was noncovalently coupled with the temperature-responsive poly(N-isopropylacrylamide) [poly(NIPAAM)] through the sequence-specific hybridization of oligonucleotides conjugated to the protein and polymer. A 20-mer oligonucleotide was covalently linked through a heterobifunctional linker to a genetically engineered streptavidin variant that contained a unique cysteine residue at the solvent-accessible site Glu 116. The complementary DNA sequence was conjugated to the end of a linear ester-activated poly(NIPAAM). The two conjugates were allowed to self-assemble in solution via hybridization of their complementary DNA sequences. The streptavidin-poly(NIPAAM) complex could be used to affinity-precipitate radiolabeled biotin or biotinylated alkaline phosphatase above 32 degrees C through the thermally induced phase separation activity of the poly(NIPAAM). The streptavidin-oligo species could then be reversibly separated from the precipitated polymer-oligo conjugate and recycled by lowering the salt concentration, which results in denaturation of the short double-stranded DNA connection. The use of oligonucleotides to couple polymer to streptavidin allows for selective precipitation of different polymers and streptavidin complexes based on the sequence-specific hybridization of their oligonucleotide appendages. 相似文献
82.
Allozyme variation at eleven loci encoding seven enzyme systems were examined in 20 populations of diploid (genome AA, 2n = 16)Scilla scilloides in China. In comparison with the average species of seed plants studied, populations of this species display a high amount of genetic variation (A = 2.0, P = 58.6%, Ho = 0.172, and He = 0.185). Allozyme variation pattern revealed predominant outcrossing within populations and considerable differentiation (FST = 0.314) among populations as well as between the subtropic and temperate regions. The wide distribution, long existence and outcrossing are presumably the main factors responsible for the high genetic diversity within populations. But the gravity dispersal of seeds and pollination by small insects set limits to the increase of genetic variation within populations and promote differentiation between populations and regions. In addition, allozyme variation does not distinguishS. scilloides var.albo-viridis and suggests that subtropic populations may be considered as a genetic entity. 相似文献
83.
Effect of exogenous spermidine on polyamine metabolism in water hyacinth leaves under mercury stress 总被引:3,自引:0,他引:3
The influence of exogenous spermidine (Spd) on arginine decarboxylase (ADC), ornithine decarboxylase (ODC), polyamine oxidase
(PAO) activities and polyamines (PAs), proline contents in water hyacinth leaves under Mercury (Hg) stress was investigated
after 6 days treatment. The results showed that free putrescine (Put) content increased, the contents of free spermidine (Spd)
and spermine (Spm) and the (Spd + Spm)/Put ratio in water hyacinth leaves decreased significantly with the increase of the
Hg concentrations. Hg stress also disturbed the activities of ADC, ODC and PAO and caused changes on proline content. Compared
to the Hg-treatment only, exogenous Spd (0.1 mM) significantly reduced the accumulation of free Put, increased the contents
of free Spd and Spm and the ratio of (Spd + Spm)/Put in water hyacinth leaves. Furthermore, exogenous Spd enhanced the activities
of ADC, ODC and PAO and significantly increased proline content. The PS-conjugated PAs and PIS-bound PAs changed in the same
trend as free PAs. These results suggest that exogenous Spd can alleviate the metabolic disturbance of polyamines caused by
Hg in water hyacinth leaves. 相似文献
84.
Gao Kai Liu Meiyou Li Yuan Wang Lei Zhao Chao Zhao Xian Zhao Jinyi Ding Yi Tang Haifeng Jia Yanyan Wang Jingwen Wen Aidong 《Journal of molecular histology》2021,52(3):449-459
Journal of Molecular Histology - Currently, the excessive activation of N-methyl-D-aspartate receptors (NMDARs) is considered to be a crucial mechanism of brain injury. Lycium barbarum A (LyA) is a... 相似文献
85.
Yongwen Qi Hongliang Zhang Dongling Zhang Meixing Wang Junli Sun Li Ding Fenghua Wang Zichao Li 《遗传学报》2009,36(5):305-312
To assess the indica-japonica differentiation of improved rice varieties, a total of 512 modem varieties including 301 indica and 211 japonica accessions were analyzed using 36 microsatellites. The Fst coefficients ranged from 0.002 to 0.730 among the loci with an average of 0.315. Significant differentiation was detected at 94.4% of the loci studied (P 〈 0.05, pairwise Fst tests), indicating that there was a high level of indica-japonica differentiation within the improved varieties. At 18 loci, about 74%-98% of the alleles of indica and japonica accessions were distributed in two ranges of amplicon length. Linkage disequilibrium analysis showed that the distribution trends were significantly nonrandomly associated. Using the differentiation trends at the 18 loci, microsatellite index (MI) was proposed for discrimination of the two subspecies. When rice accessions with MI value greater than zero were classified as indica, and those with MI value smaller than zero were classified as japonica, about 96.1% of the accessions could be classified. This result agrees with the classification based on morphological-physiological characters, indicating that this method is feasible and effective. 相似文献
86.
Profilin‐1 (Pfn1), a ubiquitously expressed actin‐binding protein, has gained interest in epithelial‐derived cancer because of its downregulation in expression in various adenocarcinoma. Pfn1 overexpression impairs tumorigenic ability of human breast cancer xenografts thus suggesting that Pfn1 could be a tumor‐suppressor protein. The objective of the present study was to determine how Pfn1 overexpression affects cell‐cycle progression of breast cancer cells. We show that Pfn1 overexpression in MDA‐MB‐231 breast cancer cells causes cell‐cycle arrest in G1 phase and dramatically reduced proliferation in culture. Pfn1 overexpression results in increased protein stability of p27kip1 (p27—a major cyclin‐dependent kinase inhibitor) and marked elevation in the overall cellular level of p27. Proliferation defect of Pfn1 overexpressers can be partly rescued by silencing p27 expression thus suggesting a critical role of p27 in Pfn1‐induced growth inhibition of MDA‐MB‐231 cells. Finally, Pfn1 overexpression was found to sensitize MDA‐MB‐231 cells to apoptosis in response to cytotoxic stimulus thus suggesting for the first time that survival of breast cancer cells can also be negatively influenced by Pfn1 upregulation. These findings may provide novel insights underlying Pfn1's tumor‐suppressive action. J. Cell. Physiol. 223:623–629, 2010. © 2010 Wiley‐Liss, Inc. 相似文献
87.
Min Yang Yu Zhang Lei Qi Xinyue Mei Jingjing Liao Xupo Ding Weiping Deng Limin Fan Xiahong He Jorge M. Vivanco Chengyun Li Youyong Zhu Shusheng Zhu 《PloS one》2014,9(12)
Background
Intercropping systems could increase crop diversity and avoid vulnerability to biotic stresses. Most studies have shown that intercropping can provide relief to crops against wind-dispersed pathogens. However, there was limited data on how the practice of intercropping help crops against soil-borne Phytophthora disease.Principal Findings
Compared to pepper monoculture, a large scale intercropping study of maize grown between pepper rows reduced disease levels of the soil-borne pepper Phytophthora blight. These reduced disease levels of Phytophthora in the intercropping system were correlated with the ability of maize plants to form a “root wall” that restricted the movement of Phytophthora capsici across rows. Experimentally, it was found that maize roots attracted the zoospores of P. capsici and then inhibited their growth. When maize plants were grown in close proximity to each other, the roots produced and secreted larger quantities of 2,4-dihydroxy-7-methoxy-2H-1,4-benzoxazin-3(4H)-one (DIMBOA) and 6-methoxy-2-benzoxazolinone (MBOA). Furthermore, MBOA, benzothiazole (BZO), and 2-(methylthio)-benzothiazole (MBZO) were identified in root exudates of maize and showed antimicrobial activity against P. capsici.Conclusions
Maize could form a “root wall” to restrict the spread of P. capsici across rows in maize and pepper intercropping systems. Antimicrobe compounds secreted by maize root were one of the factors that resulted in the inhibition of P. capsici. These results provide new insights into plant-plant-microbe mechanisms involved in intercropping systems. 相似文献88.
Dongmei Chen Qinwei Song Runan Zhu Yuan Qian Yu Sun Jie Deng Fang Wang Yaxin Ding Run Tian Chuanhe Liu Wenjing Zhu Linqing Zhao 《中国病毒学》2017,32(2):171-174
<正>Dear Editor,Cumulative evidence supports the role of early-life viral infections,especially respiratory syncytial virus(RSV)and human rhinovirus(HRV),as major antecedents of childhood asthma(Lemanske,2002;Jackson et al.,2008).In this study,the x TAG respiratory viral panel FAST(RVP FAST)assay,a multiplex polymerase chain reaction(PCR)-based method(Arens et al.,2010;BaladaLlasat et al.,2011;Gharabaghi et al.,2011;Selvaraju,2012),was used to investigate the association of infec- 相似文献
89.
Sidong Yang Wenyuan Ding Dalong Yang Tixin Gu Feng Zhang Di Zhang Yapeng Sun Lei Ma Yanli Song 《PloS one》2013,8(11)
Purpose
The purpose of this study was to describe the epidemiology of cervical spine injury in the patients with cervical trauma and analyze its associated risk factors during the special heating season in North China.Methods
This cross-sectional study investigated predictors for cervical spine injury in cervical trauma patients using retrospectively collected data of Hebei Provincial Orthopaedic Hospital from 11/2011 to 02/2012, and 11/2012 to 02/2013. Binary logistic regression analysis was used to determine risk factors for cervical fractures/dislocations or cord injury.Results
A total of 106 patients were admitted into this study. Of all, 34 patients (32.1%) were treated from 11/2011 to 02/2012 and 72 patients (67.9%) from 11/2012 to 02/2013. The mean age was 41.9±13.3 years old; 85 patients (80.2%) were male and 82 (77.4%) from rural areas. Eighty patients (75.5%) were caused by fall including 45 (42.5%) by severe fall (>2 m). Sixty-five patients (61.3%) of all suffered injuries to other body regions and 32 (30.2%) got head injury. Thirty-one patients (29.2%) sustained cervical cord injury with cervical fractures/dislocations. Twenty-six (83.9%) of cervical cord injury patients were from rural areas and 24 (77.4%) of those resulted from fall including 15 (48.4%) from severe fall (>2 m). Logistic regression displayed that age (OR, 1.47; 95% CI, 1.05–2.07), head injury (OR, 5.63; 95% CI, 2.23–14.26), were risk factors for cervical cord injury and snowing (OR, 8.25; 95% CI, 2.26–30.15) was a risk factor for cervical spine injury due to severe fall (>2 m).Conclusions
The elder male patients and patients with head trauma are high-risk population for cervical cord injury. As a seasonal factor, snowing during heating season is of note a risk factor for cervical spine injury resulting from severe fall (>2 m) in the patients with cervical trauma in North China. 相似文献90.
Zhigang Ren Guangying Cui Haifeng Lu Xinhua Chen Jianwen Jiang Hui Liu Yong He Songming Ding Zhenhua Hu Weilin Wang Shusen Zheng 《PloS one》2013,8(10)