全文获取类型
收费全文 | 393篇 |
免费 | 0篇 |
国内免费 | 1篇 |
专业分类
系统科学 | 3篇 |
理论与方法论 | 4篇 |
现状及发展 | 50篇 |
研究方法 | 58篇 |
综合类 | 203篇 |
自然研究 | 76篇 |
出版年
2020年 | 1篇 |
2019年 | 1篇 |
2018年 | 2篇 |
2014年 | 2篇 |
2013年 | 2篇 |
2012年 | 33篇 |
2011年 | 92篇 |
2010年 | 10篇 |
2009年 | 2篇 |
2008年 | 12篇 |
2007年 | 23篇 |
2006年 | 14篇 |
2005年 | 16篇 |
2004年 | 16篇 |
2003年 | 24篇 |
2002年 | 27篇 |
2001年 | 8篇 |
2000年 | 7篇 |
1999年 | 8篇 |
1997年 | 1篇 |
1995年 | 1篇 |
1992年 | 7篇 |
1990年 | 1篇 |
1989年 | 6篇 |
1988年 | 6篇 |
1987年 | 3篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1984年 | 2篇 |
1982年 | 2篇 |
1981年 | 3篇 |
1980年 | 6篇 |
1979年 | 2篇 |
1978年 | 5篇 |
1977年 | 6篇 |
1976年 | 5篇 |
1975年 | 2篇 |
1974年 | 3篇 |
1973年 | 3篇 |
1971年 | 3篇 |
1970年 | 6篇 |
1969年 | 3篇 |
1968年 | 5篇 |
1967年 | 2篇 |
1966年 | 2篇 |
1965年 | 2篇 |
1964年 | 2篇 |
1957年 | 3篇 |
排序方式: 共有394条查询结果,搜索用时 218 毫秒
91.
92.
Global CO2 emission forecasts span such a wide range as to yield little guidance for climate policy and analysis. But global per capita emissions appear to be better constrained than total emissions, which we argue has an economic justification. Trend stationarity of per capita emissions may provide a means of characterizing the relative likelihood of global forecasts. On data spanning 1950 to 2009 a unit root hypothesis allowing for endogenous structural breaks is rejected, but adding in the 2010 observation pushes the p‐value slightly over 0.1. Since structural breaks cannot be detected at the end of sample this may simply indicate a power problem. Using Monte Carlo simulations we conclude that the lower half of a well‐known suite of IPCC emission scenarios is more likely to occur than the upper half, and the top quartile is particularly difficult to justify. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
93.
Presented herein is an index to approximately 800 authors of vascular plant names of Utah. A standardized abbreviation is presented for each author. These are listed alphabetically. Following each abbreviation is the full name and birth and death dates (where available) of each individual. In some cases the date of publication is given when biographical information is not known. 相似文献
94.
95.
96.
Zhang J Grindley JC Yin T Jayasinghe S He XC Ross JT Haug JS Rupp D Porter-Westpfahl KS Wiedemann LM Wu H Li L 《Nature》2006,441(7092):518-522
Haematopoietic stem cells (HSCs) must achieve a balance between quiescence and activation that fulfils immediate demands for haematopoiesis without compromising long-term stem cell maintenance, yet little is known about the molecular events governing this balance. Phosphatase and tensin homologue (PTEN) functions as a negative regulator of the phosphatidylinositol-3-OH kinase (PI(3)K)-Akt pathway, which has crucial roles in cell proliferation, survival, differentiation and migration. Here we show that inactivation of PTEN in bone marrow HSCs causes their short-term expansion, but long-term decline, primarily owing to an enhanced level of HSC activation. PTEN-deficient HSCs engraft normally in recipient mice, but have an impaired ability to sustain haematopoietic reconstitution, reflecting the dysregulation of their cell cycle and decreased retention in the bone marrow niche. Mice with PTEN-mutant bone marrow also have an increased representation of myeloid and T-lymphoid lineages and develop myeloproliferative disorder (MPD). Notably, the cell populations that expand in PTEN mutants match those that become dominant in the acute myeloid/lymphoid leukaemia that develops in the later stages of MPD. Thus, PTEN has essential roles in restricting the activation of HSCs, in lineage fate determination, and in the prevention of leukaemogenesis. 相似文献
97.
Stanley Salthe 《Foundations of Science》2012,17(1):9-11
The canonical developmental trajectory (CDT), as represented in this paper is both conservative and emergentist. Emerging
modes of existence, as new informational constraints, require the material continuation of prior modes upon which they are
launched. Informational constraints are material configurations. The paper is not meant to be a direct critique of existing
views within science, but an oblique one presented as an alternative, developmental model. 相似文献
98.
Productivity in crosses involving two independent reciprocal translocations in Blattella germanica are reported. Lethal effects alone could not account for the reductions in hatch since completely unproductive crosses occurred frequently. The latter are attributed to the inability of reduced numbers of viable embryos to force open the egg case. The implications for genetic control of the joint dominant effects from embryonic trapping and translocation semisterility are discussed. 相似文献
99.
H A Ross 《Experientia》1978,34(4):538-539
From the dialysis rate of a small amount of tracer hormone from a serum sample through a semipermeable membrane towards an identical serum sample, the free hormone fraction can be calculated. This method is free from a number of artefacts that may occur in equilibrium dialysis. 相似文献
100.
Regulated apoptosis is essential for both the development and the subsequent maintenance of the immune system. Interleukins, including IL-2, IL-4, IL-7 and IL-15, heavily influence lymphocyte survival during the vulnerable stages of VDJ rearrangement and later in ensuring cellular homeostasis, but the genes specifically responsible for the development and maintenance of lymphocytes have not been identified. The antiapoptotic protein MCL-1 is an attractive candidate, as it is highly regulated, appears to enhance short-term survival and functions at an apical step in genotoxic deaths. However, Mcl-1 deficiency results in peri-implantation lethality. Here we show that mice conditional for Mcl-1 display a profound reduction in B and T lymphocytes when MCL-1 is removed. Deletion of Mcl-1 during early lymphocyte differentiation increased apoptosis and arrested the development at pro-B-cell and double-negative T-cell stages. Induced deletion of Mcl-1 in peripheral B- and T-cell populations resulted in their rapid loss. Moreover, IL-7 both induced and required MCL-1 to mediate lymphocyte survival. Thus, MCL-1, which selectively inhibits the proapoptotic protein BIM, is essential both early in lymphoid development and later on in the maintenance of mature lymphocytes. 相似文献