全文获取类型
收费全文 | 240篇 |
免费 | 0篇 |
专业分类
系统科学 | 2篇 |
现状及发展 | 71篇 |
研究方法 | 30篇 |
综合类 | 136篇 |
自然研究 | 1篇 |
出版年
2018年 | 1篇 |
2016年 | 1篇 |
2013年 | 5篇 |
2012年 | 12篇 |
2011年 | 15篇 |
2010年 | 2篇 |
2009年 | 1篇 |
2008年 | 4篇 |
2007年 | 8篇 |
2006年 | 3篇 |
2005年 | 15篇 |
2004年 | 8篇 |
2003年 | 4篇 |
2002年 | 6篇 |
2001年 | 7篇 |
2000年 | 10篇 |
1999年 | 7篇 |
1996年 | 1篇 |
1992年 | 5篇 |
1991年 | 5篇 |
1990年 | 4篇 |
1989年 | 2篇 |
1987年 | 6篇 |
1986年 | 4篇 |
1985年 | 3篇 |
1984年 | 2篇 |
1983年 | 4篇 |
1982年 | 3篇 |
1981年 | 5篇 |
1980年 | 4篇 |
1979年 | 2篇 |
1978年 | 4篇 |
1977年 | 2篇 |
1976年 | 4篇 |
1975年 | 4篇 |
1974年 | 5篇 |
1973年 | 6篇 |
1972年 | 9篇 |
1971年 | 9篇 |
1970年 | 8篇 |
1969年 | 6篇 |
1968年 | 6篇 |
1967年 | 4篇 |
1966年 | 6篇 |
1965年 | 2篇 |
1964年 | 1篇 |
1959年 | 1篇 |
1958年 | 2篇 |
1957年 | 1篇 |
1955年 | 1篇 |
排序方式: 共有240条查询结果,搜索用时 0 毫秒
171.
Zusammenfassung Die Wirkung von induzierten Undeutlichkeiten auf die Reaktionsfähigkeit der Zellen im visuellen Kortex auf Bewegungsanregungen werden beschrieben.
This work was supported by USPHS Grant No. EY00576. 相似文献
This work was supported by USPHS Grant No. EY00576. 相似文献
172.
Plasma protease inhibitors in mouse and man: divergence within the reactive centre regions 总被引:5,自引:0,他引:5
The plasma protease inhibitors control a wide variety of physiological functions including blood coagulation, complement activation and aspects of the inflammatory response. The inhibitors function by forming a 1:1 complex with a specific protease within the reactive centre region of the inhibitor. Little is known about the evolutionary relationships of these inhibitors. We report here the sequences of cDNAs which represent the C-terminal halves of the two major murine plasma protease inhibitors. One of these, murine alpha 1-antitrypsin, more appropriately called alpha 1-proteinase inhibitor (alpha 1-PI), has diverged from its human counterpart at a vital position in the reactive centre but this has not led to a physiologically significant change in function. Also, we have determined the partial sequence of a recently characterized protein termed contrapsin, which inhibits trypsin-like proteases. We show, surprisingly, that contrapsin is highly homologous to human alpha 1-antichymotrypsin, an inhibitor of chymotrypsin-like proteases. The reactive centre regions of these two inhibitors have diverged considerably, which may account for the differences in specificity. We propose that the genes for contrapsin and human alpha 1-antichymotrypsin are the descendents of a single gene that have evolved since rodent and primate divergence to encode proteins with different functions. 相似文献
173.
174.
175.
176.
The analytical investigation of a damped power system has been made based on Holmes and Marsden's theorems. The condition for the occurrence of chaotic motions in the system is that the damping factor has to possess negative values. The numerical simulation results concur very well with theoretical predictions. 相似文献
177.
Accelerated evolution in the reactive centre regions of serine protease inhibitors 总被引:14,自引:0,他引:14
The serine protease inhibitors (serpins) are a family of proteins that function to control the action of serine proteases in many diverse physiological processes. The functional region or reactive centre of these inhibitors is near the C-terminal end and is an exposed site that acts as a bait for the appropriate serine protease to recognize and covalently bind. The specificity of the inhibitor is determined, at least in part, by a single amino acid that resides in this region at the P1 position. We show here that following a gene duplication event the reactive centres of three related rodent protease inhibitors have diverged from each other at unprecedented rates. This has resulted in proteins with different predicted specificities and we postulate that these changes were fixed by positive darwinian selection and that the most likely selective forces are extrinsic proteases, namely those used by parasites to facilitate their spread throughout the host. 相似文献
178.
Tagliaferri G Goad M Chincarini G Moretti A Campana S Burrows DN Perri M Barthelmy SD Gehrels N Krimm H Sakamoto T Kumar P Mészáros PI Kobayashi S Zhang B Angelini L Banat P Beardmore AP Capalbi M Covino S Cusumano G Giommi P Godet O Hill JE Kennea JA Mangano V Morris DC Nousek JA O'Brien PT Osborne JP Pagani C Page KL Romano P Stella L Wells A 《Nature》2005,436(7053):985-988
'Long' gamma-ray bursts (GRBs) are commonly accepted to originate in the explosion of particularly massive stars, which give rise to highly relativistic jets. Inhomogeneities in the expanding flow result in internal shock waves that are believed to produce the gamma-rays we see. As the jet travels further outward into the surrounding circumstellar medium, 'external' shocks create the afterglow emission seen in the X-ray, optical and radio bands. Here we report observations of the early phases of the X-ray emission of five GRBs. Their X-ray light curves are characterised by a surprisingly rapid fall-off for the first few hundred seconds, followed by a less rapid decline lasting several hours. This steep decline, together with detailed spectral properties of two particular bursts, shows that violent shock interactions take place in the early jet outflows. 相似文献
179.
Hill MT Dorren HJ De Vries T Leijtens XJ Den Besten JH Smalbrugge B Oei YS Binsma H Khoe GD Smit MK 《Nature》2004,432(7014):206-209
The increasing speed of fibre-optic-based telecommunications has focused attention on high-speed optical processing of digital information. Complex optical processing requires a high-density, high-speed, low-power optical memory that can be integrated with planar semiconductor technology for buffering of decisions and telecommunication data. Recently, ring lasers with extremely small size and low operating power have been made, and we demonstrate here a memory element constructed by interconnecting these microscopic lasers. Our device occupies an area of 18 x 40 microm2 on an InP/InGaAsP photonic integrated circuit, and switches within 20 ps with 5.5 fJ optical switching energy. Simulations show that the element has the potential for much smaller dimensions and switching times. Large numbers of such memory elements can be densely integrated and interconnected on a photonic integrated circuit: fast digital optical information processing systems employing large-scale integration should now be viable. 相似文献
180.
As lithospheric plates are subducted, rocks are metamorphosed under high-pressure and ultrahigh-pressure conditions to produce eclogites and eclogite facies metamorphic rocks. Because chemical equilibrium is rarely fully achieved, eclogites may preserve in their distinctive mineral assemblages and textures a record of the pressures, temperatures and deformation the rock was subjected to during subduction and subsequent exhumation. Radioactive parent-daughter isotopic variations within minerals reveal the timing of these events. Here we present in situ zircon U/Pb ion microprobe data that dates the timing of eclogite facies metamorphism in eastern Papua New Guinea at 4.3 +/- 0.4 Myr ago, making this the youngest documented eclogite exposed at the Earth's surface. Eclogite exhumation from depths of approximately 75 km was extremely rapid and occurred at plate tectonic rates (cm yr(-1)). The eclogite was exhumed within a portion of the obliquely convergent Australian-Pacific plate boundary zone, in an extending region located west of the Woodlark basin sea floor spreading centre. Such rapid exhumation (> 1 cm yr(-1)) of high-pressure and, we infer, ultrahigh-pressure rocks is facilitated by extension within transient plate boundary zones associated with rapid oblique plate convergence. 相似文献