全文获取类型
收费全文 | 974篇 |
免费 | 102篇 |
国内免费 | 33篇 |
专业分类
1109篇 |
出版年
2024年 | 27篇 |
2023年 | 9篇 |
2022年 | 14篇 |
2021年 | 10篇 |
2020年 | 51篇 |
2019年 | 46篇 |
2018年 | 43篇 |
2017年 | 41篇 |
2016年 | 20篇 |
2015年 | 20篇 |
2014年 | 52篇 |
2013年 | 77篇 |
2012年 | 51篇 |
2011年 | 47篇 |
2010年 | 27篇 |
2009年 | 46篇 |
2008年 | 42篇 |
2007年 | 50篇 |
2006年 | 32篇 |
2005年 | 30篇 |
2004年 | 20篇 |
2003年 | 22篇 |
2002年 | 15篇 |
2001年 | 22篇 |
2000年 | 15篇 |
1999年 | 16篇 |
1998年 | 18篇 |
1997年 | 17篇 |
1996年 | 24篇 |
1995年 | 15篇 |
1994年 | 18篇 |
1993年 | 16篇 |
1992年 | 13篇 |
1991年 | 13篇 |
1990年 | 16篇 |
1989年 | 9篇 |
1988年 | 14篇 |
1987年 | 14篇 |
1986年 | 12篇 |
1985年 | 12篇 |
1984年 | 14篇 |
1983年 | 6篇 |
1982年 | 7篇 |
1981年 | 7篇 |
1980年 | 3篇 |
1979年 | 4篇 |
1977年 | 3篇 |
1975年 | 4篇 |
1974年 | 1篇 |
1973年 | 4篇 |
排序方式: 共有1109条查询结果,搜索用时 10 毫秒
41.
42.
This study provides the most comprehensive physico-chemical and phytoplankton data yet available for Australian dune lakes,
which are among the world's most naturally acidic and oligotrophic freshwaters. Seasonal and spatial variations were examined
in Blue Lagoon and Lake Freshwater, two ‘water-table window’ lakes in south-east Queensland. Like other dune lakes, they are
acidic (minimum pH 4.20 and 4.55, respectively), polymictic water bodies with low concentrations of marine-derived major ions
and almost undetectable levels of trace metals. While linmologically similar in winter, during spring-summer Lake Freshwater
has significantly higher levels of chlorophyll-a, total phosphorus (TP) and turbidity than Blue Lagoon and other dune lakes, indicating seasonal mesotrophy. The key nutrient
is TP, which has recently increased to a maximum of 17 μ· l−1, due either to inputs from recreational sources, or to the death and decomposition of littoral vegetation resulting from
falling water levels over the last decade. Inorganic nitrogen, though present only in small amounts, does not appear to limit
the eutrophication process because of a shift in phytoplankton dominance from the usual desmids and dinoflagellates to N2-fixing blue-green algae.
A chlorophyll - TP linear regression derived for dune lakes indicates that at TP < 20 μg · l−1 chlorophyll ‘yield’ is higher than in other lake types represented by regressions from the literature. This may be due to
a more efficient utilization of the limited available phosphorus by dune lake algae which have adapted to the naturally oligotrophic
environment. The implications of these findings for lake management are discussed. 相似文献
43.
Keita Nishiyama Akira Kawanabe Hirofumi Miyauchi Fumiaki Abe Daigo Tsubokawa Kazuhiko Ishihara 《Bioscience, biotechnology, and biochemistry》2013,77(8):1444-1451
The aim of this study was to assess the adhesion of Bifidobacterium strains to acidic carbohydrate moieties of porcine colonic mucin. Mucins were extracted and purified via gel filtration chromatography followed by density-gradient ultracentrifugation. The presence of sulfated and sialylated carbohydrates in mucins was shown by enzyme-linked immunosorbent assays using PGM34 and HMC31 monoclonal antibodies (mAbs), respectively. Adhesion of Bifidobacterium strains to mucin preparations was markedly affected by the degree of purification. In eight of 22 strains, we observed increased adhesion to mucin preparations purified by ultracentrifugation. Moreover, in some of these eight strains, adhesion to mucin was reduced by pretreatment with sulfatase and/or sialidase, and competitively inhibited by pretreatment with PGM34 and/or HCM31 mAbs. Our results showed that some Bifidobacterium strains adhered to sulfo- and/or sialomucin and were able to recognize carbohydrate structures of the mAbs epitopes. 相似文献
44.
Yaoyu Ren Timo Danner Alexandra Moy Martin Finsterbusch Tanner Hamann Jan Dippell Till Fuchs Marius Müller Ricky Hoft André Weber Larry A. Curtiss Peter Zapol Matthew Klenk Anh T. Ngo Pallab Barai Brandon C. Wood Rongpei Shi Liwen F. Wan Tae Wook Heo Martin Engels Jagjit Nanda Felix H. Richter Arnulf Latz Venkat Srinivasan Jürgen Janek Jeff Sakamoto Eric D. Wachsman Dina Fattakhova-Rohlfing 《Liver Transplantation》2023,13(1):2201939
The garnet-type phase Li7La3Zr2O12 (LLZO) attracts significant attention as an oxide solid electrolyte to enable safe and robust solid-state batteries (SSBs) with potentially high energy density. However, while significant progress has been made in demonstrating compatibility with Li metal, integrating LLZO into composite cathodes remains a challenge. The current perspective focuses on the critical issues that need to be addressed to achieve the ultimate goal of an all-solid-state LLZO-based battery that delivers safety, durability, and pack-level performance characteristics that are unobtainable with state-of-the-art Li-ion batteries. This perspective complements existing reviews of solid/solid interfaces with more emphasis on understanding numerous homo- and heteroionic interfaces in a pure oxide-based SSB and the various phenomena that accompany the evolution of the chemical, electrochemical, structural, morphological, and mechanical properties of those interfaces during processing and operation. Finally, the insights gained from a comprehensive literature survey of LLZO–cathode interfaces are used to guide efforts for the development of LLZO-based SSBs. 相似文献
45.
Robert J. Wall Caird E. Rexroad Jr. Anne Powell Avi Shamay Robert McKnight Lothar Hennighausen 《Transgenic research》1996,5(1):67-72
The synthesis of foreign proteins can be targeted to the mammary gland of transgenic animals, thus permitting commercial purification of otherwise unavailable proteins from milk. Genetic regulatory elements from the mouse whey acidic protein (WAP) gene have been used successfully to direct expression of transgenes to the mammary gland of mice, goats and pigs. To extend the practical usefulness of WAP promoter-driven fusion genes and further characterize WAP expression in heterologous species, we introduced a 6.8 kb DNA fragment containing the genomic form of the mouse WAP gene into sheep zygotes. Two lines of transgenic sheep were produced. The transgene was expressed in mammary tissue of both lines and intact WAP was secreted into milk at concentrations estimated to range from 100 to 500 mg/litre. Ectopic WAP gene expression was found in salivary gland, spleen, liver, lung, heart muscle, kidney and bone marrow of one founder ewe. WAP RNA was not detected in skeletal muscle and intestine. These data suggest that unlike pigs, sheep may possess nuclear factors in a variety of tissues that interact with WAP regulatory sequences. Though the data presented are based on only two lines, these findings suggest WAP regulatory sequences may not be suitable as control elements for transgenes in sheep bioreactors. 相似文献
46.
C Klein-Soyer G Archipoff A Beretz J P Cazenave 《Biology of the cell / under the auspices of the European Cell Biology Organization》1992,75(2):155-162
The effects on vascular wound repair in vitro of aFGF and TGF-beta, growth factors having opposite influences on endothelial cell growth and angiogenesis, were studied using as a model a mechanical lesion of confluent endothelium. Modulation by heparin of the activities of these growth factors during the repair process was also examined. Whereas heparin alone inhibited repair by lowering both cell proliferation and cell migration, TGF-beta alone mainly inhibited cell proliferation. When added together, TGF-beta and heparin exerted a combined inhibitory effect resulting in a residual lesion 50% larger than in controls. aFGF alone accelerated lesion coverage and this effect was enhanced by 40% over control values when heparin was added with aFGF. This acceleration was slightly (less than 10%) but consistently diminished by TGF-beta. Cell density in confluent unwounded areas was increased by 40% in the presence of aFGF, but TGF-beta diminished cell density by 20%. A small (30%) increase in intracellular cAMP was measured whenever aFGF was present during the repair process. In comparison, intracellular cAMP inducing agents (forskolin, dbcAMP) accelerated cell migration by 20% during lesion recovery without affecting cell proliferation or density. The present results show that the inhibitory effects of TGF-beta during vascular wound repair are opposed by aFGF. Furthermore, heparin (or heparan sulfates in vivo) modulates growth factors having activating or inhibiting functions and thus plays a regulatory role during the repair process. cAMP-inducing substances other than growth factors are able to accelerate cell migration. 相似文献
47.
Jun Zhang Da‐Wei Wang Wei Lv Lei Qin Shuzhang Niu Siwei Zhang Tengfei Cao Feiyu Kang Quan‐Hong Yang 《Liver Transplantation》2018,8(26)
Sodium‐ion batteries (SIBs) have the potential to be practically applied in large‐scale energy storage markets. The rapid progress of SIBs research is primarily focused on electrodes, while electrolytes attract less attention. Indeed, the improvement of electrode performance is arguably correlated with the electrolyte optimization. In conventional lithium‐ion batteries (LIBs), ether‐based electrolytes are historically less practical owing to the insufficient passivation of both anodes and cathodes. As an important class of aprotic electrolytes, ethers have revived with the emerging lithium‐sulfur and lithium‐oxygen batteries in recent years, and are even booming in the wave of SIBs. Ether‐based electrolytes are unique to enabling these new battery chemistries in terms of producing stable ternary graphite intercalation compounds, modifying anode solid electrolyte interphases, reducing the solubility of intermediates, and decreasing polarization. Better still, ether‐based electrolytes are compatible with specific inorganic cathodes and could catalyze the assembly of full SIBs prototypes. This Research News article aims to summarize the recent critical reports on ether‐based electrolytes in sodium‐based batteries, to unveil the uniqueness of ether‐based electrolytes to advancing diverse electrode materials, and to shed light on the viability and challenges of ether‐based electrolytes in future sodium‐based battery chemistries. 相似文献
48.
Sergey Malchenko Jianping Xie Maria de Fatima Bonaldo Elio F. Vanin Bula J. Bhattacharyya Abdelhak Belmadani Guifa Xi Vasily Galat William Goossens Richard E.B. Seftor Tadanori Tomita John Crispino Richard J. Miller Martha C. Bohn Mary J.C. Hendrix Marcelo B. Soares 《Gene》2014
In vitro neural differentiation of human embryonic stem cells (hESCs) is an advantageous system for studying early neural development. The process of early neural differentiation in hESCs begins by initiation of primitive neuroectoderm, which is manifested by rosette formation, with consecutive differentiation into neural progenitors and early glial-like cells. In this study, we examined the involvement of early neural markers – OTX2, PAX6, Sox1, Nestin, NR2F1, NR2F2, and IRX2 – in the onset of rosette formation, during spontaneous neural differentiation of hESC and human induced pluripotent stem cell (hiPSC) colonies. This is in contrast to the conventional way of studying rosette formation, which involves induction of neuronal differentiation and the utilization of embryoid bodies. Here we show that OTX2 is highly expressed at the onset of rosette formation, when rosettes comprise no more than 3–5 cells, and that its expression precedes that of established markers of early neuronal differentiation. Importantly, the rise of OTX2 expression in these cells coincides with the down-regulation of the pluripotency marker OCT4. Lastly, we show that cells derived from rosettes that emerge during spontaneous differentiation of hESCs or hiPSCs are capable of differentiating into dopaminergic neurons in vitro, and into mature-appearing pyramidal and serotonergic neurons weeks after being injected into the motor cortex of NOD-SCID mice. 相似文献
49.
以小兴安岭酸性森林泥炭土为研究对象,通过加入10 mL·L-1乙炔及不同浓度的外源硫酸铵(0、1.2、6.0 mmol N·kg-1)进行硝化培养试验,探究酸性泥炭土中硝化作用类型及主要驱动因子.结果表明:无论有无外加氮源,酸性泥炭土均存在较强的矿化作用(0.9~1.4 mg N·kg-1·d-1),经过2周的培养均发生了硝化作用(0.4~0.6 mg N·kg-1·d-1),且不同浓度硫酸铵处理之间无显著差异;而乙炔处理虽有较强的矿化作用(0.8 mg N·kg-1·d-1),但未发生明显的硝化作用(0 mg N·kg-1·d-1),说明该酸性泥炭土以自养硝化为主,外源无机氮源浓度对硝化作用无显著影响,硝化底物NH3的主要来源不是外源硫酸铵,更可能来源于土壤中有机氮的矿化.培养0~14 d,无论有无外加氮源,酸性泥炭土氨氧化细菌(AOB)和古菌(AOA)丰度均显著增加,但不同浓度硫酸铵处理间无显著差异,表明外源无机氮浓度对氨氧化微生物的生长无显著促进作用.与不加乙炔的对照相比,乙炔处理AOB和AOA丰度随时间均无显著变化,推测AOA与AOB在该酸性泥炭土的硝化过程中都可能起一定的作用. 相似文献
50.
Therapeutic angiogenesis for peripheral artery disease (PAD), achieved by gene and cell therapy, has recently raised a great deal of hope for patients who cannot undergo standard revascularizing treatment. Although pre-clinical studies gave very promising data, still clinical trials of gene therapy have not provided satisfactory results. On the other hand, cell therapy approach, despite several limitations, demonstrated more beneficial effects but initial clinical studies must be constantly validated by larger randomized, multi-center, double-blinded, placebo-controlled trials. This review focuses on previous and recent gene and cell therapy studies for limb ischemia, including both experimental and clinical research, and summarizes some important papers published in this field. Moreover, it provides a short comment on combined gene and cell therapy approach on the example of heme oxygenase-1 overexpressing cells with therapeutic properties. 相似文献