全文获取类型
收费全文 | 2660篇 |
免费 | 76篇 |
国内免费 | 3篇 |
学科分类
工业技术 | 2739篇 |
出版年
2022年 | 18篇 |
2021年 | 41篇 |
2020年 | 29篇 |
2019年 | 35篇 |
2018年 | 47篇 |
2017年 | 45篇 |
2016年 | 55篇 |
2015年 | 43篇 |
2014年 | 70篇 |
2013年 | 165篇 |
2012年 | 112篇 |
2011年 | 128篇 |
2010年 | 120篇 |
2009年 | 104篇 |
2008年 | 107篇 |
2007年 | 88篇 |
2006年 | 88篇 |
2005年 | 79篇 |
2004年 | 54篇 |
2003年 | 70篇 |
2002年 | 67篇 |
2001年 | 42篇 |
2000年 | 33篇 |
1999年 | 44篇 |
1998年 | 104篇 |
1997年 | 70篇 |
1996年 | 67篇 |
1995年 | 56篇 |
1994年 | 44篇 |
1993年 | 60篇 |
1992年 | 36篇 |
1991年 | 22篇 |
1990年 | 21篇 |
1989年 | 28篇 |
1988年 | 27篇 |
1987年 | 33篇 |
1986年 | 26篇 |
1985年 | 25篇 |
1984年 | 33篇 |
1983年 | 24篇 |
1982年 | 23篇 |
1981年 | 40篇 |
1980年 | 35篇 |
1979年 | 24篇 |
1978年 | 25篇 |
1977年 | 29篇 |
1976年 | 29篇 |
1975年 | 26篇 |
1973年 | 16篇 |
1972年 | 14篇 |
排序方式: 共有2739条查询结果,搜索用时 15 毫秒
71.
Dr. Francis P. McManus Prof. Christopher J. Wilds 《Chembiochem : a European journal of chemical biology》2014,15(13):1966-1977
O6‐Alkylguanine‐DNA alkyltransferases (AGTs) are responsible for the removal of O6‐alkyl 2′‐deoxyguanosine (dG) and O4‐alkyl thymidine (dT) adducts from the genome. Unlike the E. coli OGT (O6‐alkylguanine‐DNA‐alkyltransferase) protein, which can repair a range of O4‐alkyl dT lesions, human AGT (hAGT) only removes methyl groups poorly. To uncover the influence of the C5 methyl group of dT on AGT repair, oligonucleotides containing O4‐alkyl 2′‐deoxyuridines (dU) were prepared. The ability of E. coli AGTs (Ada‐C and OGT), human AGT, and an OGT/hAGT chimera to remove O4‐methyl and larger adducts (4‐hydroxybutyl and 7‐hydroxyheptyl) from dU were examined and compared to those relating to the corresponding dT species. The absence of the C5 methyl group resulted in an increase in repair observed for the O4‐methyl adducts by hAGT and the chimera. The chimera was proficient at repairing larger adducts at the O4 atom of dU. There was no observed correlation between the binding affinities of the AGT homologues to adduct‐containing oligonucleotides and the amounts of repair measured. 相似文献
72.
Francis Narin 《Scientometrics》2012,92(2):391-393
In the almost 40?years since we wrote Evaluative bibliometrics enormous advances have been made in data availability and analytic technique. The journal impact factor of the 1960s has clearly not kept up with the state of the art. However, for both old and new indicators, basic validity and relevance issues remain, such as by what standard can we validate our results, and what external use can appropriately be made of them? As funding support becomes more difficult, we should not lose sight of the necessity to again demonstrate the importance of our research, and must keep in mind that it is the relevance of our results that count, not the elegance of our mathematics. 相似文献
73.
74.
Ilias Soumpasis Lis Alban Francis Butler 《Food research international (Ottawa, Ont.)》2012,45(2):1139-1148
Human salmonellosis is an important food-borne disease and S. Typhimurium is the most common serotype attributed to pork products. Under a farm-to-fork strategy, reducing the levels of Salmonella-positive pigs entering the slaughterhouse is an important goal. A framework model was developed, where the effect of dynamic (infection characteristics) and non-dynamic (cleanness and disinfection, biosecurity measures, etc.) factors were considered. Four baseline scenarios were created, corresponding to different levels associated with national Salmonella monitoring programs, and sensitivity analyses were run for the non-dynamic factors. Moreover, the option of vaccination was incorporated into the model, in order to provide with a tool for the formulation of an optimum vaccination strategy depending on the characteristics of the vaccine. 相似文献
75.
温压是一种可将增高密度与选择高使用性能材料相结合的技术。增高密度有助于提高零件的力学性能,以及整体使用性能。将密度增高与高使用性能相结合,可使制造的零件的使用性能超过相应的铸锻材料产品,同时可制成具有最终形的零件,从而显著减低生产成本。因此,自动变速器的涡轮毂就成为了温压的一个理想对象。这篇论文将评述,将用于高扭矩自动变速器的常规锻件切削加工的涡轮毂转换为用一次压制/一次烧结制造的粉末冶金涡轮毂。粉末冶金涡轮毂使用的材料是FD-0405。在试验室对这种扩散合金化材料进行了评价,和报告了几个密度水平的力学性能。温压可使高应力的内花键区全面达到高密度。为了证明粉末冶金零件的适用性,进行了广泛的力学与零件的特定试验。 相似文献
76.
Benjamin W. Riblett Nicola L. Francis Margaret A. Wheatley Ulrike G. K. Wegst 《Advanced functional materials》2012,22(23):4920-4923
Successful spinal cord repair is thought to be promoted with hierarchically structured scaffolds. These should combine aligned porosity with additional linear features on the micrometer scale to guide axons across multiple length scales. Such scaffolds are generated through the carefully controlled directional solidification of an aqueous biopolymer solution, followed by lyophilization. Under specific freezing conditions this yields a highly regular and aligned lamellar architecture. This architecture exhibits uniform ridges of controlled height and width on the lamellar surface. These ridges run parallel to the pore axis, serving as secondary guidance features. The ridges are capable of linearly aligning 62.4% of chick dorsal root ganglia neurites to within ±10° of the ridge direction. Notably, neurites sprouting perpendicular to the ridge are guided into alignment with these microridged features. 相似文献
77.
78.
Francis Kofi Andoh-Baidoo Kweku-Muata Osei-Bryson Kwasi Amoako-Gyampah 《Information Systems Frontiers》2012,14(2):237-259
We explore the theoretical foundations on how firm and IT characteristics explain the market value variations in e-commerce
initiatives by examining the announcements of 946 e-commerce initiatives in the public media. Our approach combines the Event
study methodology and Decision tree induction to examine the main and interaction effects of IT and firm characteristics on
Cumulative Abnormal Returns (CAR). In particular, we generate complex interaction models that can guide e-commerce investment
decisions so managers can know, for example, which combination of IT and firm characteristics are more likely to be viewed
positively by investors. The selected study variables as well as explanation of the proposed framework are informed by innovation,
resource-based view, transaction cost economics and complementarity theories. We have inductively developed a set of propositions
that can be deductively tested to assess the validity of our proposed theoretical framework. Hence our study provides an initial
roadmap for theory development on e-commerce and CAR. 相似文献
79.
Ihebrodike M. Mejeha Michael C. Nwandu Kelechukwu B. Okeoma Lebe A. Nnanna Maduabuchi A. Chidiebere Francis C. Eze Emeka E. Oguzie 《Journal of Materials Science》2012,47(6):2559-2572
The adsorption of Aspilia africana extract and subsequent corrosion inhibition of aluminium alloy AA3003 in hydrochloric acid solutions have been investigated
using gravimetric and electrochemical techniques. Inhibition efficiency increased with extract concentration and temperature
rise. Polarization studies revealed that the extract essentially inhibited the cathodic reaction. An adsorption mechanism
involving physisorption and chemisorption of extract constituents at low and high temperatures, respectively, has been proposed
from the trend of adsorption-free energies. Quantum chemical computations and molecular dynamics simulations described the
individual contributions of some extract constituents to the observed inhibiting effect. 相似文献
80.
James Eberwine Ditte Lovatt Peter Buckley Hannah Dueck Chantal Francis Tae Kyung Kim Jaehee Lee Miler Lee Kevin Miyashiro Jacqueline Morris Tiina Peritz Terri Schochet Jennifer Spaethling Jai-Yoon Sul Junhyong Kim 《Journal of the Royal Society Interface》2012,9(77):3165-3183
The building blocks of complex biological systems are single cells. Fundamental insights gained from single-cell analysis promise to provide the framework for understanding normal biological systems development as well as the limits on systems/cellular ability to respond to disease. The interplay of cells to create functional systems is not well understood. Until recently, the study of single cells has concentrated primarily on morphological and physiological characterization. With the application of new highly sensitive molecular and genomic technologies, the quantitative biochemistry of single cells is now accessible. 相似文献