首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   19419篇
  免费   1433篇
  国内免费   1347篇
  22199篇
  2024年   52篇
  2023年   289篇
  2022年   630篇
  2021年   1063篇
  2020年   710篇
  2019年   890篇
  2018年   801篇
  2017年   615篇
  2016年   882篇
  2015年   1254篇
  2014年   1473篇
  2013年   1508篇
  2012年   1756篇
  2011年   1532篇
  2010年   955篇
  2009年   816篇
  2008年   947篇
  2007年   766篇
  2006年   729篇
  2005年   573篇
  2004年   526篇
  2003年   470篇
  2002年   407篇
  2001年   372篇
  2000年   341篇
  1999年   312篇
  1998年   204篇
  1997年   188篇
  1996年   174篇
  1995年   152篇
  1994年   115篇
  1993年   105篇
  1992年   132篇
  1991年   110篇
  1990年   96篇
  1989年   58篇
  1988年   46篇
  1987年   49篇
  1986年   25篇
  1985年   26篇
  1984年   16篇
  1983年   20篇
  1982年   4篇
  1980年   4篇
  1979年   1篇
  1978年   1篇
  1977年   1篇
  1974年   1篇
  1972年   1篇
  1966年   1篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
21.
Developing a titanium dioxide (TiO2)‐based anode with superior high‐rate capability and long‐term cycling stability is important for efficient energy storage. Herein, a simple one‐step approach for fabricating blue TiO2 nanoparticles with oxygen vacancies is reported. Oxygen vacancies can enlarge lattice spaces, lower charge transfer resistance, and provide more active sites in TiO2 lattices. As a result, this blue TiO2 electrode exhibits a highly reversible capacity of 50 mAh g?1 at 100 C (16 800 mA g?1) even after 10 000 cycles, which is attributable to the combination of surface capacitive process and remarkable diffusion‐controlled insertion revealed by the kinetic analysis. The strategy of employing oxygen‐deficient nanoparticles may be extended to the design of other robust semiconductor materials as electrodes for energy storage.  相似文献   
22.
Castration-resistant progression of prostate cancer after androgen deprivation therapies remains the most critical challenge in the clinical management of prostate cancer. Resurgent androgen receptor (AR) activity is an established driver of castration-resistant progression, and upregulation of the full-length AR (AR-FL) and constitutively-active AR splice variants (AR-Vs) has been implicated to contribute to the resurgent AR activity. We reported previously that ginsenoside 20(S)-protopanaxadiol-aglycone (PPD) can reduce the abundance of both AR-FL and AR-Vs. In the present study, we further showed that the effect of PPD on AR expression and target genes was independent of androgen. PPD treatment resulted in a suppression of ligand-independent AR transactivation. Moreover, PPD delayed castration-resistant regrowth of LNCaP xenograft tumors after androgen deprivation and inhibited the growth of castration-resistant 22Rv1 xenograft tumors with endogenous expression of AR-FL and AR-Vs. This was accompanied by a decline in serum prostate-specific antigen levels as well as a decrease in AR levels and mitoses in the tumors. Notably, the 22Rv1 xenograft tumors were resistant to growth inhibition by the next-generation anti-androgen enzalutamide. The present study represents the first to show the preclinical efficacy of PPD in inhibiting castration-resistant progression and growth of prostate cancer. The findings provide a rationale for further developing PPD or its analogues for prostate cancer therapy.  相似文献   
23.
Brassinolide (BL) alleviates salt injury in cotton seedlings; however, little is known about the molecular mechanisms of this response. In this study, digital gene expression analysis was performed to better understand the regulatory pathways of BL in NaCl-stressed cotton (Gossypium hirsutum L.). Compared with control plants (CK), a total of 1 162 and 7 659 differentially expressed genes (DEGs) were detected in the leaves and roots of NaCl-treated plants, respectively. Most of the DEGs in NaCl-treated plants, compared to CK, were regulated by BL. Moreover, expression patterns of DEGs in BL+NaCl treated plants were similar to those in CK plants; however, the responses of DEGs in the leaves and roots of NaCl-treated plants to BL differed. In the roots, BL-regulated DEGs were involved in protein biosynthesis, whereas in the leaves, BL promoted photosynthesis in NaCl-stressed cotton. BL treatment also significantly increased the overall biomass, chlorophyll a + b content in leaves, and the protein content in roots in NaCl-stressed cotton. The downregulation of stress-responsive genes in BL+NaCl-stressed leaves was also found. These results suggest that BL can alleviate NaCl injury in cotton plants.  相似文献   
24.
The role of hydrogen peroxide (H(2)O(2)) in abscisic acid (ABA)-induced anthocyanin accumulation in detached and intact leaves of rice seedlings was investigated. Treatment with ABA resulted in an accumulation of anthocyanins in detached rice leaves. Dimethylthiourea, a chemical trap for H(2)O(2), was observed to be effective in inhibiting ABA-induced accumulation of anthocyanins. Inhibitors of NADPH oxidase (diphenyleneiodonium chloride and imidazole), phosphatidylinositol 3-kinase (wortmannin and LY 294002), and a donor of nitric oxide (N-tert-butyl-alpha-phenylnitrone), which have previously been shown to prevent ABA-induced H(2)O(2) accumulation in detached rice leaves, inhibited ABA-induced anthocyanin increase. Exogenous application of H(2)O(2), however, was found to increase the anthocyanin content of detached rice leaves. In terms of H(2)O(2) accumulation, intact (attached) leaves of rice seedlings of cultivar Taichung Native 1 (TN1) are ABA sensitive and those of cultivar Tainung 67 (TNG67) are ABA insensitive. Upon treatment with ABA, H(2)O(2) and anthocyanins accumulated in leaves of TN1 seedlings but not in leaves of TNG67. Our results, obtained from detached and intact leaves of rice seedlings, suggest that H(2)O(2) is involved in ABA-induced anthocyanin accumulation in this species.  相似文献   
25.
26.
Present work reported the cloning and characterization of a human novel RNA binding gene Partner of NOB1 (PNO1), with a length of 1637bp and a putative open reading frame of 759 bp, isolated from human kidney. It is composed of seven exons and is localized on chromosome 2p14. Western blot showed that the molecular weight of PNO1 is about 35kDa. RT-PCR results in 16 human tissues indicated that PNO1 is expressed mainly in liver, lung, spleen and kidney, slightly in thymus, testis, ovary, respectively, but not in heart, brain, skeletal muscle, placenta, pancreas, prostate, small intestine, colon and peripheral blood leukocytes. GFP fusion expression in mammalian cells exhibited its localization in the nucleus, especially in nucleoli. Subcellular localization of thirteen GFP fusion PNO1 deletion proteins showed that the region of 92-230 aa is solely responsible for its nucleolar retention, and KH domain alone is not sufficient for nucleolar retention. The PNO1 family shows significant conservation in both eukaryotes and prokaryotes.  相似文献   
27.
Previous studies have demonstrated changes in plant growth and reproduction in response to nutrient availability, but responses of plant growth and reproduction to multiple levels of nutrient enrichment remain unclear. In this study, a factorial field experiment was performed with manipulation of nitrogen (N) and phosphorus (P) availability to examine seed production of the dominant species, Stipa krylovii, in response to N and P addition in a temperate steppe. There were three levels of N and P addition in this experiment, including no N addition (0 g N m−2 year−1), low N addition (10 g N m−2 year−1), and high N addition (40 g N m−2 year−1) for N addition treatment, and no P addition (0 g P m−2 year−1), low P addition (5 g P m−2 year−1), and high P addition (10 g P m−2 year−1) for P addition treatment. Low N addition enhanced seed production by 814%, 1371%, and 1321% under ambient, low, and high P addition levels, respectively. High N addition increased seed production by 2136%, 3560%, and 3550% under ambient, low, and high P addition levels, respectively. However, P addition did not affect seed production in the absence of N addition, but enhanced it under N addition. N addition enhanced seed production mainly by increasing the tiller number and inflorescence abundance per plant, whereas P addition stimulated it by decreasing the plant density yet stimulating height of plants and their seed number per inflorescence. Our results indicate seed production is not limited by P availability but rather by N availability in the temperate steppe, whereas seed production will be increased by P addition when N availability is improved. These findings enable a better understanding of plant reproduction dynamics in the temperate steppe under intensified nutrient enrichment and can inform their improved management in the future.  相似文献   
28.
Diao Y  Guo X  Li Y  Sun K  Lu L  Jiang L  Fu X  Zhu H  Sun H  Wang H  Wu Z 《Cell Stem Cell》2012,11(2):231-241
In mouse skeletal muscles, Pax7 uniquely marks muscle satellite cells and plays some important yet unknown functions at the perinatal stage. To elucidate its in vivo functions, we initiated a yeast two-hybrid screening to look for Pax7-interacting proteins and identified a previously uncharacterized Pax7- and Pax3-binding protein (Pax3/7BP). Pax3/7BP is a ubiquitously expressed nuclear protein, enriched in Pax7+ muscle precursor cells (MPCs), and serves as an indispensable adaptor for Pax7 to recruit the histone 3 lysine 4 (H3K4) methyltransferase (HMT) complex by bridging Pax7 and Wdr5. Knockdown of Pax3/7BP abolished the Pax3/7-associated H3K4 HMT activity and inhibited the proliferation of Pax7+ MPCs from young mice both in culture and in vivo. Id3 and Cdc20 were direct target genes of Pax7 and Pax3/7BP involved in the proliferation of Pax7+ MPCs. Collectively, our work establishes Pax3/7BP as an essential adaptor linking Pax3/7 with the H3K4 HMT to regulate the proliferation of MPCs.  相似文献   
29.
Limited information is available regarding the role of endogenous Glial cell line-derived neurotrophic factor (GDNF) in the spinal cord following transection injury. The present study investigated the possible role of GDNF in injured spinal cords following transection injury (T9–T10) in adult rats. The locomotor function recovery of animals by the BBB (Basso, Beattie, Bresnahan) scale score showed that hindlimb support and stepping function increased gradually from 7 days post operation (dpo) to 21 dpo. However, the locomotion function in the hindlimbs decreased effectively in GDNF-antibody treated rats. GDNF immunoreactivty in neurons in the ventral horn of the rostral stump was stained strongly at 3 and 7 dpo, and in the caudal stump at 14 dpo, while immunostaining in astrocytes was also seen at all time-points after transection injury. Western blot showed that the level of GDNF protein underwent a rapid decrease at 7 dpo in both stumps, and was followed by a partial recovery at a later time-point, when compared with the sham-operated group. GDNF mRNA-positive signals were detected in neurons of the ventral horn, especially in lamina IX. No regenerative fibers from corticospinal tract can be seen in the caudal segment near the injury site using BDA tracing technique. No somatosensory evoked potentials (SEP) could be recorded throughout the experimental period as well. These findings suggested that intrinsic GDNF in the spinal cord could play an essential role in neuroplasticity. The mechanism may be that GDNF is involved in the regulation of local circuitry in transected spinal cords of adult rats.  相似文献   
30.
Guo T  Liu X  Wan X  Weng J  Liu S  Liu X  Chen M  Li J  Su N  Wu F  Cheng Z  Guo X  Lei C  Wang J  Jiang L  Wan J 《植物学报(英文版)》2011,53(8):598-607
High chalkiness is a major problem in many rice-producing areas of the world, especially in hybrid rice (Oryza sativa L.) in China. We previously showed a major quantitative trait locus for the percentage of grains with white chalkiness (QTLqPGWC-8) in the interval G1149-R727 on chromosome 8 using a chromosome segment substitution line (CSSL). Here, we selected the line-CSSL50 harboring the QTLqPGWC-8 allele from the CSSLs derived from a cross between Asominori (as a recurrent parent) and IR24 (as a donor parent), which had higher percentage chalkiness, markedly different from that of Asominori. There were also significant differences in starch granules, appearance of amylose content (AAC) and milling qualities between Asominori and CSSL50, but not in grain size or thousand grain weight (TGW). The BC(4) F(2) and BC(4) F(3) populations from a cross between CSSL50 and Asominori were used for fine mapping of qPGWC-8. We narrowed down the location of this QTL to a 142 kb region between Indel markers 8G-7 and 8G-9. QTLqPGWC-8 accounted for 50.9% of the difference in PGWC between the parents. The markers tightly linked to qPGWC-8 should facilitate cloning of the gene underlying this QTL and will be of value for marker-assisted selection in breeding rice varieties with better grain quality.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号