全文获取类型
收费全文 | 22240篇 |
免费 | 137篇 |
国内免费 | 57篇 |
专业分类
系统科学 | 240篇 |
丛书文集 | 268篇 |
教育与普及 | 32篇 |
理论与方法论 | 146篇 |
现状及发展 | 10349篇 |
研究方法 | 889篇 |
综合类 | 10268篇 |
自然研究 | 242篇 |
出版年
2013年 | 142篇 |
2012年 | 407篇 |
2011年 | 652篇 |
2010年 | 142篇 |
2008年 | 314篇 |
2007年 | 330篇 |
2006年 | 389篇 |
2005年 | 566篇 |
2004年 | 963篇 |
2003年 | 795篇 |
2002年 | 469篇 |
2001年 | 591篇 |
2000年 | 613篇 |
1999年 | 418篇 |
1992年 | 334篇 |
1991年 | 262篇 |
1990年 | 283篇 |
1989年 | 271篇 |
1988年 | 242篇 |
1987年 | 269篇 |
1986年 | 306篇 |
1985年 | 381篇 |
1984年 | 277篇 |
1983年 | 250篇 |
1982年 | 242篇 |
1981年 | 240篇 |
1980年 | 267篇 |
1979年 | 681篇 |
1978年 | 558篇 |
1977年 | 538篇 |
1976年 | 387篇 |
1975年 | 463篇 |
1974年 | 688篇 |
1973年 | 558篇 |
1972年 | 597篇 |
1971年 | 662篇 |
1970年 | 814篇 |
1969年 | 670篇 |
1968年 | 638篇 |
1967年 | 639篇 |
1966年 | 541篇 |
1965年 | 449篇 |
1964年 | 145篇 |
1959年 | 197篇 |
1958年 | 337篇 |
1957年 | 255篇 |
1956年 | 190篇 |
1955年 | 196篇 |
1954年 | 199篇 |
1948年 | 131篇 |
排序方式: 共有10000条查询结果,搜索用时 429 毫秒
231.
232.
233.
234.
235.
236.
Zhitao Xu X. G. Ming Wenyan Song Lina He Miao Li 《Systemic Practice and Action Research》2014,27(2):141-164
Quite often over the last decade, heavy equipment manufacturers are trying to improve their project management performance with the use of effective project management methods. However, the challenges encountered aren’t isolated problems and a systemic approach is required. This paper exemplifies how a systemic approach can be applied to heavy equipment manufacturing project (HEMP) management, through of a multifaceted vision. The findings present in the paper are based on a two-year case study in a metallurgic equipment manufacturing enterprise in China. Based on the analysis of HEMP management problems and the contributions on systemic approach application in project management, the paper enriches existing theory by: (1) interpreting the HEMP management system with the top-down disassembly method; (2) developing the collaborative project management approach with a systems view highlighting the project characteristics management and inter-departmental collaboration; (3) making suggestions for systemic approach application in project management. For practitioners and researchers, the findings are particularly meaningful for manufacturing project management and systemic approach application. 相似文献
237.
Pau B. Esparza-Moltó Cristina Nuevo-Tapioles José M. Cuezva 《Cellular and molecular life sciences : CMLS》2017,74(12):2151-2166
The mitochondrial H+-ATP synthase is a primary hub of cellular homeostasis by providing the energy required to sustain cellular activity and regulating the production of signaling molecules that reprogram nuclear activity needed for adaption to changing cues. Herein, we summarize findings regarding the regulation of the activity of the H+-ATP synthase by its physiological inhibitor, the ATPase inhibitory factor 1 (IF1) and their functional role in cellular homeostasis. First, we outline the structure and the main molecular mechanisms that regulate the activity of the enzyme. Next, we describe the molecular biology of IF1 and summarize the regulation of IF1 expression and activity as an inhibitor of the H+-ATP synthase emphasizing the role of IF1 as a main driver of energy rewiring and cellular signaling in cancer. Findings in transgenic mice in vivo indicate that the overexpression of IF1 is sufficient to reprogram energy metabolism to an enhanced glycolysis and activate reactive oxygen species (ROS)-dependent signaling pathways that promote cell survival. These findings are placed in the context of mitohormesis, a program in which a mild mitochondrial stress triggers adaptive cytoprotective mechanisms that improve lifespan. In this regard, we emphasize the role played by the H+-ATP synthase in modulating signaling pathways that activate the mitohormetic response, namely ATP, ROS and target of rapamycin (TOR). Overall, we aim to highlight the relevant role of the H+-ATP synthase and of IF1 in cellular physiology and the need of additional studies to decipher their contributions to aging and age-related diseases. 相似文献
238.
239.
Paloma Feyjoo Miguel Cabanellas-Reboredo Matías Calvo-Manazza Beatriz Morales-Nín Jorge Hernández-Urcera Manuel E. Garci 《Journal of Natural History》2016,50(9-10):543-555
The embryonic development of the squid Loligo vulgaris was observed from 183 egg masses collected from special devices deployed throughout Cabrera National Park (Baleares Islands, western Mediterranean Sea). Sequence alignment analysis of the cytochrome oxidase I gene revealed that all embryos belonged to L. vulgaris. In total, 549 egg capsules were examined. Viable egg capsules (n = 420) were classified into one of five maturation stages according to the primary external features. The length of the viable egg capsules varied between 40 and 170 mm, and increased with embryonic development. The non-viable capsules (n = 129) were categorized into four groups: I (Ginger root), non-viable II and III, and empty egg capsule (IV). The percentage of non-viable capsules (i.e. grades I, II and III) was 92.25%. Empty capsules accounted for 7.75% of the total non-viable egg capsules. Embryonic development was classified into a second scale of eight stages. Egg capsule stage and embryonic stage were significantly related (n = 420; p < 0.001), facilitating the determination of the embryo developmental phase based on the outward appearance of the egg capsules. The embryo development stage based on the external features of the egg capsules might constitute an innovative tool for in situ embryological data collection. This new method is neither time consuming nor invasive, and could be helpful in fishing cruises, for scuba diving visual census in natural habitats and for laboratory culture. Slight variability in the developmental embryonic stages within egg capsules from the same egg mass was identified. The origin of this asynchrony is discussed. Chronological appearance of organs was similar to that of the six loliginid species previously examined. However, some developmental changes in the timing or rate of events (heterochronies) were observed: Hoyle’s organ was formed earlier in L. vulgaris and the appearance of ventral chromatophores was slightly delayed (2 days) compared with the other species considered. 相似文献
240.
Miguel Bernabé-Rubio Miguel A. Alonso 《Cellular and molecular life sciences : CMLS》2017,74(22):4077-4095
Primary cilia are solitary, microtubule-based protrusions of the cell surface that play fundamental roles as photosensors, mechanosensors and biochemical sensors. Primary cilia dysfunction results in a long list of developmental and degenerative disorders that combine to give rise to a large spectrum of human diseases affecting almost any major body organ. Depending on the cell type, primary ciliogenesis is initiated intracellularly, as in fibroblasts, or at the cell surface, as in renal polarized epithelial cells. In this review, we have focused on the routes of primary ciliogenesis placing particular emphasis on the recently described pathway in renal polarized epithelial cells by which the midbody remnant resulting from a previous cell division event enables the centrosome for initiation of primary cilium assembly. The protein machinery implicated in primary cilium formation in epithelial cells, including the machinery best known for its involvement in establishing cell polarity and polarized membrane trafficking, is also discussed. 相似文献