全文获取类型
收费全文 | 13004篇 |
免费 | 1182篇 |
国内免费 | 9篇 |
学科分类
工业技术 | 14195篇 |
出版年
2024年 | 37篇 |
2023年 | 133篇 |
2022年 | 455篇 |
2021年 | 1089篇 |
2020年 | 449篇 |
2019年 | 456篇 |
2018年 | 507篇 |
2017年 | 527篇 |
2016年 | 580篇 |
2015年 | 477篇 |
2014年 | 621篇 |
2013年 | 941篇 |
2012年 | 904篇 |
2011年 | 1011篇 |
2010年 | 773篇 |
2009年 | 734篇 |
2008年 | 679篇 |
2007年 | 618篇 |
2006年 | 486篇 |
2005年 | 359篇 |
2004年 | 314篇 |
2003年 | 268篇 |
2002年 | 257篇 |
2001年 | 166篇 |
2000年 | 106篇 |
1999年 | 136篇 |
1998年 | 111篇 |
1997年 | 119篇 |
1996年 | 111篇 |
1995年 | 81篇 |
1994年 | 63篇 |
1993年 | 63篇 |
1992年 | 66篇 |
1991年 | 48篇 |
1990年 | 45篇 |
1989年 | 37篇 |
1988年 | 36篇 |
1987年 | 33篇 |
1986年 | 41篇 |
1985年 | 37篇 |
1984年 | 28篇 |
1983年 | 25篇 |
1982年 | 17篇 |
1981年 | 16篇 |
1980年 | 21篇 |
1979年 | 22篇 |
1978年 | 20篇 |
1977年 | 14篇 |
1976年 | 8篇 |
1975年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
Konstantin V. Dergilev Evgeny K. Shevchenko Zoya I. Tsokolaeva Irina B. Beloglazova Ekaterina S. Zubkova Maria A. Boldyreva Mikhail Yu. Menshikov Elizaveta I. Ratner Dmitry Penkov Yelena V. Parfyonova 《International journal of molecular sciences》2020,21(24)
Cell therapy of the post-infarcted myocardium is still far from clinical use. Poor survival of transplanted cells, insufficient regeneration, and replacement of the damaged tissue limit the potential of currently available cell-based techniques. In this study, we generated a multilayered construct from adipose-derived mesenchymal stromal cells (MSCs) modified to secrete stem cell factor, SCF. In a rat model of myocardium infarction, we show that transplantation of SCF producing cell sheet induced activation of the epicardium and promoted the accumulation of c-kit positive cells in ischemic muscle. Morphometry showed the reduction of infarct size (16%) and a left ventricle expansion index (0.12) in the treatment group compared to controls (24–28%; 0.17–0.32). The ratio of viable myocardium was more than 1.5-fold higher, reaching 49% compared to the control (28%) or unmodified cell sheet group (30%). Finally, by day 30 after myocardium infarction, SCF-producing cell sheet transplantation increased left ventricle ejection fraction from 37% in the control sham-operated group to 53%. Our results suggest that, combining the genetic modification of MSCs and their assembly into a multilayered construct, we can provide prolonged pleiotropic effects to the damaged heart, induce endogenous regenerative processes, and improve cardiac function. 相似文献
42.
43.
44.
45.
Identification of vivianite,an unusual blue pigment,in a sixteenth century painting and its implications
下载免费PDF全文
![点击此处可从《Color research and application》网站下载免费的PDF全文](/ch/ext_images/free.gif)
António João Cruz Erica Eires Luís Dias Teresa Desterro Carla Rego 《Color research and application》2018,43(2):177-183
Vivianite, a blue pigment employed in the past practically only in Northern and Central Europe, but with very limited use, was identified in an early sixteenth century painting, stylistically with Flemish features, from a church in Portugal. The identification of this iron phosphate mineral was made by SEM‐EDS based on the atomic ratio between phosphorus and iron in layers of blue paint (area analysis) and in particles of these same layers (spot analysis). This painting, about which there is no document to prove its authorship, becomes the first case, known in detail, of a sixteenth century painting containing vivianite. Moreover, this find and the presence of a chalk ground, also identified, strongly support the hypothesis of being a Flemish painting. 相似文献
46.
47.
This review article is devoted to the materials containing niobium, which have been discovered or developed in the past few years and exhibit the potential application in heterogeneous catalysis. Niobium oxides and mixed oxides as well as sulfides, nitrides (oxynitrides), carbides (oxycarbides), and phosphates are considered. Among the catalytic processes in which Nb-containing materials were tested, liquid and gas phase oxidation is described in details, and the role of niobium in the prevention of the catalyst from SO2 poisoning is mentioned. 相似文献
48.
An approach is presented to satisfy the demand for simple criteria, guidelines and models for the preliminary sizing of horizontal subsurface flow (SF) constructed wetland systems. This approach eliminates time-consuming calculations and iterations by providing graphical solutions for wetland system sizing. Therefore, it can be used for the preliminary assessment of new or performance evaluation of existing subsurface flow constructed wetland systems. The validity of this methodology is checked with data from existing systems and is found to be quite satisfactory. This methodology is combined with simple equations predicting the maximum wetland capacity in summer, so as to assist designers in sizing installations in tourist areas with increased summer populations. Furthermore, based on this methodology, a sensitivity analysis is performed of the area requirements for wastewaters of various strengths and various design conditions and performance criteria. The results provide a useful overview to engineers and further simplify the design methodology of new subsurface flow constructed wetland systems. 相似文献
49.
This paper addresses the problem of power control in a multihop wireless network supporting multicast traffic. We face the problem of forwarding packet traffic to multicast group members while meeting constraints on the signal-to-interference-plus-noise ratio (SINR) at the intended receivers. First, we present a distributed algorithm which, given the set of multicast senders and their corresponding receivers, provides an optimal solution when it exists, which minimizes the total transmit power. When no optimal solution can be found for the given set of multicast senders and receivers, we introduce a distributed, joint scheduling and power control algorithm which eliminates the weak connections and tries to maximize the number of successful multicast transmissions. The algorithm allows the other senders to solve the power control problem and minimize the total transmit power. We show that our distributed algorithm converges to the optimal solution when it exists, and performs close to centralized, heuristic algorithms that have been proposed to address the joint scheduling and power control problem. 相似文献
50.
Optical packet assembly is a key function to support inter-working between TCP/IP networks and optical packet-switched networks.
It is characterized by the assembly delay and by the segment aggregation needed to form an optical packet. These counter-balancing
aspects depend on several environment variables, such as the TCP parameters, the access link speed, the optical packet size
whose effects are studied in this paper. Performance evaluations are obtained by extensive simulations in terms of send rate
of TCP flows, fairness, efficiency, and assembly delay. Some guidelines in the design of optical packets that take into account
the results presented are given. 相似文献