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   5251篇
  免费   229篇
  国内免费   304篇
系统科学   244篇
丛书文集   142篇
教育与普及   88篇
理论与方法论   18篇
现状及发展   47篇
研究方法   24篇
综合类   5219篇
自然研究   2篇
  2024年   29篇
  2023年   60篇
  2022年   95篇
  2021年   87篇
  2020年   78篇
  2019年   18篇
  2018年   55篇
  2017年   66篇
  2016年   64篇
  2015年   113篇
  2014年   169篇
  2013年   156篇
  2012年   161篇
  2011年   175篇
  2010年   155篇
  2009年   207篇
  2008年   237篇
  2007年   244篇
  2006年   196篇
  2005年   183篇
  2004年   135篇
  2003年   131篇
  2002年   125篇
  2001年   161篇
  2000年   174篇
  1999年   329篇
  1998年   284篇
  1997年   283篇
  1996年   272篇
  1995年   228篇
  1994年   183篇
  1993年   174篇
  1992年   151篇
  1991年   146篇
  1990年   128篇
  1989年   101篇
  1988年   92篇
  1987年   68篇
  1986年   44篇
  1985年   13篇
  1984年   2篇
  1983年   1篇
  1982年   3篇
  1978年   1篇
  1974年   2篇
  1971年   1篇
  1967年   2篇
  1957年   2篇
排序方式: 共有5784条查询结果,搜索用时 140 毫秒
941.
The microstructure and crack behaviour of twinning induced plasticity (TWIP) steel during tensile deformation was investigated with in-situ scanning electron microscopy (SEM). The results show that there are two modes of plastic deformation during tensile test in the Fe-Mn-C TWIP steel: dislocation gliding and deformation twins. During the process of tensile deformation, secondary deformed twins are found. Inclusions have played a role in the course of ductile fracture, and microcracks initiate from inclusions and twin-twin intersections.  相似文献   
942.
As an industry-university cooperative project, an experimental research was conducted to develop a new cold-rolled transformation-induced plasticity (TRIP) steel with a tensile strength of 780 MPa and an elongation of 25% under the conditions that some processing parameters were preestablished according to the actual conditions of factory production lines. The optimal heat treatment conditions for obtaining excellent strength-ductility balance, specifically in intercritical annealing temperature and isothermal treatment temperature, were investigated by means of thermal simulation tests. Ultimately the desirable mechanical properties were attained successfully, and the microstructure and retained austenite stability were studied by optical microscopy (OM) and electron back-scattered diffraction (EBSD). It has been discovered that the sizes of retained austenite grains are generally proportional to the sizes of carbon-clear space (ferrite and bainite) around them, and there is marked selectivity in their transition sequences under stress-strain.  相似文献   
943.
实施积极的健康老龄化战略,确保所有老年人“老有所养、病有所医、老有所乐、老有所为”是老年群体公平分享社会经济发展成果的诉求,也是不断改善民生、增进国民福利的保障。运筹发展西藏老年服务产业不仅能应对即将到来的“少子老龄化”社会带来的一系列棘手问题,使老年人能健康快乐地安度晚年,以促进代际、代内公平和社会和谐。而且,老年服务产业在实现养老风险社会化分担从而减轻家庭养老压力的同时,还能创造大量的就业岗位和拉动社会需求。为此,文章提出西藏老年服务产业发展的基本思路:政府支持、战略牵引、需求导向、人文关怀、社会参与。  相似文献   
944.
To determine whether conventional hyperthermia (42-45℃) or ablation therapy (>50℃) achieves better synergistic effects on direct cytotoxicity and anti-tumor immunity,we compared the therapeutic effects of two hyperthermia temperatures,43 and 55℃,in terms of cytotoxicity and upregulation of immune functions in a mouse malignant melanoma model.Melanoma-bearing mice were treated by directly applying regional hyperthermia to the tumor nodule with a heating light at a temperature of 43℃ for 30 min or 55℃ for 10 min.The tumor growth curve and mice survival rate were observed.To investigate the hyperthermia-induced immunological response,peripheral blood CD4~+ and CD8~+ T cells and the serum IL-2 level were determined.Our results indicated that application of regional hyperthermia at the ablation temperature (such as 55℃) achieved better synergistic anti-tumor effects than did conventional hyperthermia (43℃).Significant increases in the number of peripheral blood CD4~+ T cells and the serum IL-2 level likely contributed to the underlying mechanism.  相似文献   
945.
Due to their physiology and organ size, pigs have significant potential as human disease models and as organ transplantation donors. Genetic modification of pigs could provide benefits for both agriculture and human medicine. In this study, five fetal pig fibroblast cell lines from two species (Wuzhishan and Landrace pigs) were transfected using double-marked human lysozyme (HLY) plasmids (pBC1-HLY-GFP-NEO) by a liposome-mediated method. The ratio of green fluorescent protein (GFP)-expressing cells was >95% in sw7, sw8, slw3 and slw6 cell lines, but only 49.3% in slw9 cells. Cells from the four highly transgenic lines were used as nuclear donors to construct embryos, which were then cultured after fusion and activation by electric stimulation. The rate of cleavage was 76.7%, 48 h after activation. After 7 days, 18.5% of cleaved eggs had developed to the blastocyst stage and 93.3% of blastocysts were GFP-positive. These results indicate that transgenic fetal pig fibroblast cell lines could be obtained by a liposome-mediated method, though the transfection efficiency varied between cell lines. Reconstructed embryos derived from transgenic cells could successfully develop into blastocysts, most of which were GFP-positive.  相似文献   
946.
湖南省科技中介服务发展现状及其发展建议   总被引:2,自引:1,他引:1  
一个功能较完善、机构充分发展、服务质量较高的科技中介服务体系,是区域创新体系不可或缺的重要组成部分,是推进地区新型工业化、构建特色区域知识经济体系的重要支撑。当前,湖南科技中介机构的发展与创新需求还存在很大差距,认识不到位、体系不完善、基础薄弱、服务质量不高、社会信誉度偏低、相关政策法规体系不完善等问题较突出。加强科技中介机构的自身服务能力建设,进一步规范政府部门的引导职能,努力构建湖南特色新型科技中介服务体系是建设创新型湖南的迫切需要,是加速湖南特色新型工业化进程的重要保障。  相似文献   
947.
不同温度条件下氟乐灵对茄子黄萎病的诱抗效果   总被引:1,自引:0,他引:1  
唐保宏  杨帆  陈捷 《河南科学》2009,27(8):952-954
研究了诱抗剂氟乐灵在不同温度条件下对茄子黄萎病的诱抗效果.结果表明,氟乐灵对茄子黄萎病具有较好的诱抗效果,持效期在24d以上.温度对诱抗效果和持效期具有显著影响,氟乐灵在20℃和25℃诱抗防效较佳,持效期长;而30℃时诱抗效果较差,持效期较短.控制适宜的温度可以提高诱抗剂的防效,并延长持效期.  相似文献   
948.
政府在高职教育校企合作中的功能定位和作为   总被引:2,自引:0,他引:2  
在公共服务型政府的职能框架下,分析校企合作困境中的政府因素,研究得出政府在高职院校校企合作中应担负起健全机制、建立法规、加强管理的职能,并对校企合作过程进行组织协调、扶持保障、责任监督和对校企合作成果进行评价激励的结论,为校企合作中政府的功能定位和作为提供参考。  相似文献   
949.
本文分析了在当前体育教学改革新形势下的体育教学方法中的一些问题,提出应在人本主义教育思想指导下,进行体育教学语法改革。  相似文献   
950.
Objective: To investigate the enhancive effect of N,N′-dinitrosopiperazine (DNP) on induced carcinogenesis in nasal and/or nasopharyngeal epithelia among TgN(p53mt-LMP1)/HT transgenic mice to examine the underlying mechanism for the development of nasopharyngeal carcinoma (NPC). Methods: TgN(p53mt-LMP1)/HT transgenic mice and the same strain of C57BL/6J wild-type mice both at the age of 5 months were randomly divided into 2 groups in parallel, respectively, i.e., TgN(p53mt-LMP1)/HT cancerous lesion-inducing group (TI), TgN(p53mt-LMP1)/HT control group (TC), C57BL/6J cancerous lesion-inducing group (CI), and C57BL/6J control group (CC). TI and CI mice were treated only with DNP for 16 weeks, twice each week, while TC and CC mice were given the same volume of saline as controls. At the end of treatment, animals were sacrificed to collect epithelial tissue samples from nasal cavity and nasopharynx for pathohistological evaluation by haematoxylin and eosin (HE) staining and for determination on the expression of TRAF2, c-Jun, and p16 by immunohistochemistry. Results: Atypical hyperplasia was more significant in the samples of TI than in those of TC, CI, and CC, with the rates of lesions being 90%, 10%, 0, and 0 (P<0.01) respectively, though DNP was used alone in a much shortened inducing period at less dosage and without the use of carcinogenic promoter 12-O-tetradecanoylphorbol-13-acetate as usual. The expressions of tumor necrosis factor (TNF) receptor-associated factor 2 (TRAF2) and c-Jun in these samples were significantly up-regulated in TI (P<0.01), while the expression of p16 was significantly lower in TI than in the other groups (P<0.01). Conclusion: TgN(p53mt-LMP1)/HT mice hold inherited constitutional defect in immune surveillance function, which can be aggravated by environmental carcinogens, such as DNP used even though in a much less strength. The enhanced carcinogenesis-inducing effect of DNP on TgN(p53mt-LMP1)/HT mice should be closely associated with abnormal signaling of activator protein-1 (AP-1) pathway, especially up-regulated expressions of TRAF2 and c-Jun, and down-regulated expression of p16.  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