全文获取类型
收费全文 | 153369篇 |
免费 | 2235篇 |
国内免费 | 3522篇 |
专业分类
系统科学 | 3872篇 |
丛书文集 | 3900篇 |
教育与普及 | 3013篇 |
理论与方法论 | 931篇 |
现状及发展 | 41613篇 |
研究方法 | 2094篇 |
综合类 | 101498篇 |
自然研究 | 2205篇 |
出版年
2022年 | 1173篇 |
2021年 | 1354篇 |
2015年 | 1794篇 |
2014年 | 2524篇 |
2013年 | 2846篇 |
2012年 | 3267篇 |
2011年 | 5791篇 |
2010年 | 3164篇 |
2009年 | 3679篇 |
2008年 | 4726篇 |
2007年 | 4909篇 |
2006年 | 4186篇 |
2005年 | 4223篇 |
2004年 | 4347篇 |
2003年 | 3752篇 |
2002年 | 3693篇 |
2001年 | 4184篇 |
2000年 | 3969篇 |
1999年 | 5037篇 |
1998年 | 3989篇 |
1997年 | 4186篇 |
1996年 | 3702篇 |
1995年 | 3179篇 |
1994年 | 3271篇 |
1993年 | 2898篇 |
1992年 | 3277篇 |
1991年 | 2849篇 |
1990年 | 2774篇 |
1989年 | 2457篇 |
1988年 | 2149篇 |
1987年 | 1829篇 |
1986年 | 1507篇 |
1985年 | 1505篇 |
1980年 | 1179篇 |
1979年 | 2344篇 |
1978年 | 2020篇 |
1977年 | 1982篇 |
1976年 | 1601篇 |
1975年 | 1688篇 |
1974年 | 2098篇 |
1973年 | 1985篇 |
1972年 | 2055篇 |
1971年 | 2387篇 |
1970年 | 2850篇 |
1969年 | 2361篇 |
1968年 | 2266篇 |
1967年 | 2259篇 |
1966年 | 1966篇 |
1965年 | 1478篇 |
1958年 | 1317篇 |
排序方式: 共有10000条查询结果,搜索用时 234 毫秒
1.
以西湖凹陷西斜坡花港组、平湖组致密砂岩储层为研究对象,通过录井资料分析及岩心和显微薄片观察,研究裂缝的宏观与微观发育特征及其影响因素.结果显示其主要发育层理缝和构造缝.层理缝主要为水平缝和低角度缝,且已被充填;构造缝主要为垂直缝和高角度缝,充填缝和未充填缝各占一半.裂缝的发育受岩性、单层厚度、断裂及地应力场的综合影响.在交会图法(定性)和概率判别法(半定量)研究的基础上,将岩心观察统计结果与常规测井曲线和成像测井成果相对比,综合预测与评价裂缝发育段,认为有利的裂缝发育层段为花港组下段和平湖组中下段. 相似文献
2.
This is a contribution towards a history and philosophy of modeling in its early stages in electromagnetism. In 1873, James Clerk Maxwell (1831–1879) hinted at the methodology of modeling at the end of his Treatise on Electricity and Magnetism. We focus on Maxwell's impact on physicists who immediately followed him, specifically Oliver Lodge (1851–1940) and George Francis FitzGerald (1851–1901). We begin with the role that the scientific concept of model played in the late nineteenth century, as assessed by Ludwig Boltzmann (1844–1906). We then discuss the role of hypothesis as a methodology, the appeal to (dynamical) illustration, and the way Maxwell applied model and working model in his studies of electromagnetism. We show that for Maxwell these key terms were kept distinct, but Lodge did not maintain these distinctions and, in this regard, FitzGerald followed Lodge. Notwithstanding Lodge's influence, Fitzgerald modified Maxwell's theory based on the mechanical model he designed, thereby implicitly taking the first step towards modeling. This methodology consists in drawing consequences from the (mechanical) model to the (electrodynamic) theory and modifying the latter in light of the functioning of the former. At the core of our argument is the thesis that it was a methodological novelty to move from the concept of model to the methodology of modeling. The introduction of modeling as a new methodology into physics in the late nineteenth century was a major event which deserves proper recognition. 相似文献
3.
从“十四五”保护与发展的生态关系角度,探讨了生态保护与绿色发展的十大生态关系,阐述了生态保护和绿色发展中的一系列有关生态关系的生态智慧及生态技术,并对长江、黄河等流域的生态保护和修复提出了相关建议。 相似文献
4.
近年来,我国金融行业数字化转型不断提速,金融机构数字化转型已迫在眉睫.金融机构面临的数字化转型环境包括3个方面:一是大数据走向跨界融合;二是人工智能加速发展;三是区块链等技术建立了新型连接关系.基于以上环境分析,文章认为金融机构数字化转型的核心在于业务与技术融合,需要在机制、组织、架构、人才和文化层面实行再造. 相似文献
5.
进入新发展阶段后,科技创新创业活动对孵化服务提出了更高的要求,科技创业载体需要加快提升专业化、精准化服务能力.文章基于2016-2019年全国科技创业孵化载体发展数据,全面分析专业化科技创业孵化载体建设发展现状,剖析了科技创业孵化载体在专业化建设方面存在的方向不清、动力不足、能力不够、模式不明、机制不畅等问题,从建立评价指标体系、明确建设主体、提升服务能力、加强资源开放和政策供给等方面提出对策建议. 相似文献
6.
众所周知,在《数学分析》中会遇到连续函数的一个重要定理,即根的存在定理,此定理对方程根的存在性判别起着重要作用.将这方面已有的定理进行推广,并用例题说明其应用情况. 相似文献
7.
8.
9.
J. D. Trout has recently developed a new defense of scientific realism, a new version of the No Miracles Argument. I critically evaluate Trout's novel defense of realism. I argue that Trout's argument for scientific realism and the related explanation for the success of science are self-defeating. In the process of arguing against the traditional realist strategies for explaining the success of science, he inadvertently undermines his own argument. 相似文献
10.
Lei Chen Cong-Fa Huang Yi-Cun Li Wei-Wei Deng Liang Mao Lei Wu Wen-Feng Zhang Lu Zhang Zhi-Jun Sun 《Cellular and molecular life sciences : CMLS》2018,75(11):2045-2058
The NLRP3 inflammasome is a critical innate immune pathway responsible for producing active interleukin (IL)-1β, which is associated with tumor development and immunity. However, the mechanisms regulating the inflammatory microenvironment, tumorigenesis and tumor immunity are unclear. Herein, we show that the NLRP3 inflammasome was over-expressed in human HNSCC tissues and that the IL-1β concentration was increased in the peripheral blood of HNSCC patients. Additionally, elevated NLRP3 inflammasome levels were detected in tumor tissues of Tgfbr1/Pten 2cKO HNSCC mice, and elevated IL-1β levels were detected in the peripheral blood serum, spleen, draining lymph nodes and tumor tissues. Blocking NLRP3 inflammasome activation using MCC950 remarkably reduced IL-1β production in an HNSCC mouse model and reduced the numbers of myeloid-derived suppressor cells (MDSCs), regulatory T cells (Tregs) and tumor-associated macrophages (TAMs). Moreover, inhibiting NLRP3 inflammasome activation increased the numbers of CD4+ and CD8+ T cells in HNSCC mice. Notably, the numbers of exhausted PD-1+ and Tim3+ T cells were significantly reduced. A human HNSCC tissue microarray showed that NLRP3 inflammasome expression was correlated with the expression of CD8 and CD4, the Treg marker Foxp3, the MDSC markers CD11b and CD33, and the TAM markers CD68 and CD163, PD-1 and Tim3. Overall, our results demonstrate that the NLRP3 inflammasome/IL-1β pathway promotes tumorigenesis in HNSCC and inactivation of this pathway delays tumor growth, accompanied by decreased immunosuppressive cell accumulation and an increased number of effector T cells. Thus, inhibition of the tumor microenvironment through the NLRP3 inflammasome/IL-1β pathway may provide a novel approach for HNSCC therapy. 相似文献