全文获取类型
收费全文 | 667篇 |
免费 | 48篇 |
出版年
2023年 | 9篇 |
2022年 | 22篇 |
2021年 | 42篇 |
2020年 | 18篇 |
2019年 | 17篇 |
2018年 | 26篇 |
2017年 | 16篇 |
2016年 | 37篇 |
2015年 | 29篇 |
2014年 | 26篇 |
2013年 | 55篇 |
2012年 | 40篇 |
2011年 | 42篇 |
2010年 | 28篇 |
2009年 | 31篇 |
2008年 | 34篇 |
2007年 | 33篇 |
2006年 | 22篇 |
2005年 | 28篇 |
2004年 | 22篇 |
2003年 | 19篇 |
2002年 | 18篇 |
2001年 | 12篇 |
2000年 | 8篇 |
1999年 | 2篇 |
1998年 | 6篇 |
1997年 | 3篇 |
1996年 | 4篇 |
1995年 | 2篇 |
1993年 | 4篇 |
1992年 | 5篇 |
1991年 | 4篇 |
1990年 | 9篇 |
1988年 | 2篇 |
1987年 | 3篇 |
1986年 | 4篇 |
1985年 | 3篇 |
1984年 | 4篇 |
1983年 | 3篇 |
1982年 | 5篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1978年 | 1篇 |
1977年 | 2篇 |
1974年 | 1篇 |
1973年 | 3篇 |
1972年 | 2篇 |
1969年 | 1篇 |
1941年 | 1篇 |
排序方式: 共有715条查询结果,搜索用时 15 毫秒
691.
692.
Christopher Alan Williams Niall Hanan Robert J. Scholes Werner Kutsch 《Oecologia》2009,161(3):469-480
The idea that many processes in arid and semi-arid ecosystems are dormant until activated by a pulse of rainfall, and then
decay from a maximum rate as the soil dries, is widely used as a conceptual and mathematical model, but has rarely been evaluated
with data. This paper examines soil water, evapotranspiration (ET), and net ecosystem CO2 exchange measured for 5 years at an eddy covariance tower sited in an Acacia–Combretum savanna near Skukuza in the Kruger National Park, South Africa. The analysis characterizes ecosystem flux responses to discrete
rain events and evaluates the skill of increasingly complex “pulse models”. Rainfall pulses exert strong control over ecosystem-scale
water and CO2 fluxes at this site, but the simplest pulse models do a poor job of characterizing the dynamics of the response. Successful
models need to include the time lag between the wetting event and the process peak, which differ for evaporation, photosynthesis
and respiration. Adding further complexity, the time lag depends on the prior duration and degree of water stress. ET response
is well characterized by a linear function of potential ET and a logistic function of profile-total soil water content, with
remaining seasonal variation correlating with vegetation phenological dynamics (leaf area). A 1- to 3-day lag to maximal ET
following wetting is a source of hysteresis in the ET response to soil water. Respiration responds to wetting within days,
while photosynthesis takes a week or longer to reach its peak if the rainfall was preceded by a long dry spell. Both processes
exhibit nonlinear functional responses that vary seasonally. We conclude that a more mechanistic approach than simple pulse
modeling is needed to represent daily ecosystem C processes in semiarid savannas.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
693.
694.
Mohamed Soliman El-Kholy Mohamed Mohamed El-Hindawy Mahmoud Alagawany Mohamed Ezzat Abd El-Hack Sabry Abd El-Gawad Abd El-Halim El-Sayed 《Biological trace element research》2017,177(1):148-158
Ideal coatings for orthopedic implants should be able to induce excellent osseointegration with host bone tissue, which requires good osteogenic responses and limited inflammatory reactions. Cerium oxide (CeO2) ceramics have anti-oxidative properties and can be used to decrease mediators of inflammation, making them attractive for biomedical application. In this study, two kinds of CeO2 incorporated calcium silicate coatings (CS-10Ce and CS-30Ce) were prepared via plasma spraying technique, and the effects of CeO2 addition on the responses of bone mesenchymal stem cells (BMSCs) and RAW264.7 macrophages were evaluated. The CS-10Ce and CS-30Ce coatings were characterized by X-ray diffraction, scanning electron microscopy, and X-ray photoelectron spectroscopy. An increase in CeO2 content in the coatings resulted in enhanced chemical stability and better BMSCs osteogenic behaviors in terms of cell adhesion, proliferation, ALP activity, and mineralized nodule formation. With respect to either ZrO2-added or unmodified CS coating, the CS-30Ce coating elicited higher effects on the macrophages, suppressing the gene expressions of pro-inflammatory (M1) markers (CCR7, IL-6, and TNF-α), while upregulating the expressions of anti-inflammatory (M2) markers (CD206, IL-1ra, and IL-10); moreover, it could also increase the expression of osteoinductive molecules (BMP2 and TGF-β1) by the macrophages. The results suggested that the regulation of BMSCs behaviors and macrophage-mediated responses at the coating’s surface was related to CeO2 incorporation. The incorporation of CeO2 in CS coatings can be a valuable strategy to promote osteogenic responses and mitigate inflammatory reactions. 相似文献
695.
696.
Hanan?E. Shamseldin Anna Rajab Amal Alhashem Ranad Shaheen Tarfa Al-Shidi Rana Alamro Salma Al Harassi Fowzan?S. Alkuraya 《American journal of human genetics》2013,93(3):555-560
Orofaciodigital syndrome (OFD) is a recognized clinical entity with core defining features in the mouth, face, and digits, in addition to various other features that have been proposed to define distinct subtypes. The three genes linked to OFD—OFD1, TMEM216, and TCTN3—play a role in ciliary biology, a finding consistent with the clinical overlap between OFD and other ciliopathies. Most autosomal-recessive cases of OFD, however, remain undefined genetically. In two multiplex consanguineous Arab families affected by OFD, we identified a tight linkage interval in chromosomal region 1q32.1. Exome sequencing revealed a different homozygous variant in DDX59 in each of the two families, and at least one of the two variants was accompanied by marked reduction in the level of DDX59. DDX59 encodes a relatively uncharacterized member of the DEAD-box-containing RNA helicase family of proteins, which are known to play a critical role in all aspects of RNA metabolism. We show that Ddx59 is highly enriched in its expression in the developing murine palate and limb buds. At the cellular level, we show that DDX59 is localized dynamically to the nucleus and the cytoplasm. Consistent with the absence of DDX59 representation in ciliome databases and our demonstration of its lack of ciliary localization, ciliogenesis appears to be intact in mutant fibroblasts but ciliary signaling appears to be impaired. Our data strongly implicate this RNA helicase family member in the pathogenesis of OFD, although the causal mechanism remains unclear. 相似文献
697.
Ultrastructural examination of the head kidney of Periophthalmus koelreuteri (Pallas) (Teleostei, Gobiidae) revealed that the nephronic tubule cells are bound by tight junctions and desmosomes with little intercellular space. The first proximal segment (PI) consists of low columnar cells with well developed brush borders, indented nuclei, and numerous apical endocytic vesicles and lysosomes. A second cell type possessing clusters of apical cilia and lacking brush border and lysosomes is occasionally found between PI cells. The second proximal segment (PII) is formed of high columnar cells with brush border, regular spherical nuclei and numerous mitochondria located between well developed infoldings of the basal membrane. Single ciliary structures protrude into the lumen from PI and PII cells. The distal segment is lined by low columnar epithelium with few microvilli, regular spherical nuclei, numerous scattered mitochondria, and microbodies. The collecting tubule cells are cuboidal with few euchromatic nuclei, some mitochondria, and secondary lysosomes. 相似文献
698.
Zaki Islam El-Sayed El-Sherbiny H. Radwan Eman M. 《Russian Journal of Bioorganic Chemistry》2021,47(2):514-523
Russian Journal of Bioorganic Chemistry - A new series of coumarin-derived molecules have been synthesized and evaluated for their anticancer activity against human hepatocellular liver carcinoma... 相似文献
699.
Natural products are considered a good choice in the biological control of mosquitoes because they are an effective way to eliminate larvae and prevent an increase in mosquito numbers, while simultaneously not polluting the environment or damaging health. This investigation was designed to study the potential toxicity of three species of algae, Caulerpa racemosa (Weber-van Bosse, 1909), Padina boryana (Thivy, 1966), and Turbinaria ornata (Turner J. Agardh, 1848), on the larvae of Aedes aegypti mosquito, the vector of dengue and Zika viruses. Among the studied species, Caulerpa racemosa showed the greatest effectiveness in eradicating A. aegypti larvae with an LC50 = 43.5 ppm, followed by Padina boryana with an LC50 = 51.93 ppm. Both species proved to be excellent candidates as a source of larvicidal agents and could be used commercially in mosquito control programs as eco-friendly biopesticides. The combined activity of different mixtures against mosquito larvae was expressed as the coeffective factor (C.F.). C.F. values showed that the joint activity of insect growth regulator Dudim in combination with Caulerpa racemosa and Padina boryana extracts produced degrees of potentiation effects and degrees of additive effects were obtained with Dudim in combination with Turbinaria ornata extract. 相似文献
700.
Abdulrahman Nabeel Ibrahim Meram Joseph Jensa Mariam Elkoubatry Hanan Mahmoud Al-Shamasi Al-Anood Rayan Menatallah Gadeau Alain Pierre Ahmed Rashid Eldassouki Hussein Hasan Anwarul Mraiche Fatima 《Molecular and cellular biochemistry》2022,477(6):1865-1872
Molecular and Cellular Biochemistry - Diabetes mellitus (DM)-induced cardiac morbidities have been the leading cause of death among diabetic patients. Recently, sodium-glucose cotransporter-2... 相似文献