全文获取类型
收费全文 | 13154篇 |
免费 | 1046篇 |
国内免费 | 12篇 |
专业分类
电工技术 | 85篇 |
综合类 | 8篇 |
化学工业 | 5209篇 |
金属工艺 | 158篇 |
机械仪表 | 324篇 |
建筑科学 | 471篇 |
矿业工程 | 20篇 |
能源动力 | 338篇 |
轻工业 | 3262篇 |
水利工程 | 110篇 |
石油天然气 | 72篇 |
无线电 | 488篇 |
一般工业技术 | 1804篇 |
冶金工业 | 536篇 |
原子能技术 | 40篇 |
自动化技术 | 1287篇 |
出版年
2024年 | 43篇 |
2023年 | 182篇 |
2022年 | 906篇 |
2021年 | 1034篇 |
2020年 | 427篇 |
2019年 | 437篇 |
2018年 | 499篇 |
2017年 | 509篇 |
2016年 | 565篇 |
2015年 | 465篇 |
2014年 | 617篇 |
2013年 | 960篇 |
2012年 | 861篇 |
2011年 | 963篇 |
2010年 | 762篇 |
2009年 | 705篇 |
2008年 | 637篇 |
2007年 | 587篇 |
2006年 | 448篇 |
2005年 | 334篇 |
2004年 | 283篇 |
2003年 | 255篇 |
2002年 | 239篇 |
2001年 | 142篇 |
2000年 | 97篇 |
1999年 | 132篇 |
1998年 | 112篇 |
1997年 | 112篇 |
1996年 | 109篇 |
1995年 | 75篇 |
1994年 | 62篇 |
1993年 | 60篇 |
1992年 | 68篇 |
1991年 | 47篇 |
1990年 | 38篇 |
1989年 | 35篇 |
1988年 | 36篇 |
1987年 | 32篇 |
1986年 | 44篇 |
1985年 | 38篇 |
1984年 | 34篇 |
1983年 | 22篇 |
1982年 | 17篇 |
1981年 | 20篇 |
1980年 | 22篇 |
1979年 | 19篇 |
1978年 | 24篇 |
1977年 | 16篇 |
1976年 | 11篇 |
1975年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
Worldwide, cervical cancer is the second most common cancer in women, after breast cancer. The prevalence of this malignant disease is estimated at 1.4 million cases worldwide, causing about 290,000 deaths and 500,000 new cases per year, of which 80% correspond to women living in developing countries. In this work we propose a family of ordered models for basal cells of the cervix corresponding to different stages ranging from normal cells to the formation of precancerous lesions. We analyse the first member of the family analytically and for the second member we developed a non-standard numerical method in order to extract some biological information. 相似文献
92.
The reduction of dissolved sulphur and the soluble species formed during the electrolysis of PbS dissolved in the PbCl2NaCl eutectic has been studied chronopotentiometrically. The pre-lead reduction process reported earlier[1] can now be assigned to a subsulphide species that is generated electrochemically. At higher PbS concentrations (eg 10?3 mol cm?3), elemental sulphur introduces a new reduction wave in addition to the subsulphide. The saturation solubility of sulphur is approximately proportional to the square of the PbS concentration. It has been estimated to be 2.3× 10?4 mol S cm?3 at 430°C for a melt containing 2.4× 10?3 mol PbS cm?3 in the PbCl2-NaCl eutectic. 相似文献
93.
It is commonly accepted that replacement of a portion of cement in mortar or concrete with well-dispersed silica fume reduces expansion caused by alkali silica reaction. Recently there has been much discussion that large, agglomerated particles of silica fume may actually act as alkali silica reactive aggregates, thereby increasing expansion rather than reducing it. The data in the literature, from both field and laboratory studies, are inconsistent. This prompted an extensive laboratory investigation into the alkali silica reactivity of silica fume. Results from accelerated expansion testing and microscopic investigations are presented. It was seen that some agglomerated silica fumes participate in ASR while others do not. Factors determining the reactivity of silica fume agglomerates are suggested. 相似文献
94.
Maria Augusta de Luca Taís Espíndola Machado Renan Beretta Notti Marly Maldaner Jacobi 《应用聚合物科学杂志》2004,92(2):798-803
Hybrid materials were synthesized from epoxidized (68, 43, or 14%) styrene–butadiene rubber (SBR) and the hydrolysis product of tetraethoxysilane (TEOS) in situ under ultrasonic irradiation. The products were characterized with thermal analysis (differential scanning calorimetry and thermogravimetric analysis), stress–strain tests, scanning electron microscopy (including energy‐dispersive spectrometry), and swelling in tetrahydrofuran and water. The most transparent were those prepared from SBR with the highest degree of epoxidation, whereas those obtained from less epoxidized SBR and with larger amounts of TEOS showed distinct phases that could be considered two hybrid phases (one rich in TEOS and another rich in SBR). © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 798–803, 2004 相似文献
95.
Talita da Cunha Mattos Flávia Maria Santoro Kate Revoredo Vanessa Tavares Nunes 《Computers in Industry》2014
A business process is a set of activities performed in a coordinated manner within an organizational and technical environment that is aimed toward a business goal. The flexibility of a process is related to an understanding of the unexpected events that occur when people, systems and resources interact and require adjustments. Thus, business processes must be designed to respond to information about different events and their specificity. This information defines what the literature calls “context”. To broaden the perception of context in the case of a business process, this work proposes an approach to characterize the context of a business process activity in a given domain through conceptual models structured in layers. A case study was conducted to evaluate the proposal, which provided evidence of the applicability of the model. 相似文献
96.
Maria Gust Grace Goo Jeff Wolfenstine Martha L. Mecartney 《Journal of the American Ceramic Society》1993,76(7):1681-1690
Amorphous silicate grain boundary phases of varying chemistry and amounts were added to 3Y-TZP in order to determine their influence on the superplastic behavior between 1200° and 1300°C and on the room-temperature mechanical properties. Strain rate enhancement at high temperatures was observed in 3Y-TZP containing a glassy grain boundary phase, even with as little as 0.1 wt% glass. Strain rate enhancement was greatest in 3Y-TZP with 5 wt% glass, but the room-temperature hardness, elastic modulus, and fracture toughness were degraded. The addition of glassy grain boundary phases did not significantly affect the stress exponent of 3Y-TZP, but did lower the activation energy for superplastic flow. Strain rate enhancement was highest in samples containing the grain boundary phase with the highest solubility for Y2 O3 and ZrO2 , but the strain rate did not scale inversely with the viscosity of the silicate phases. Grain boundary sliding accommodated by diffusional creep controlled by an interface reaction is proposed as the mechanism for superplastic deformation in 3Y-TZP with and without glassy grain boundary phases. 相似文献
97.
Francisco Salmerón-Miranda Birgitta Båth Henrik Eckersten Johannes Forkman Maria Wivstad 《Nutrient Cycling in Agroecosystems》2007,79(2):125-139
The main objective of this field study was to estimate the total plant uptake of soil mineral N in maize (Zea mays L.) and common bean (Phaseolus vulgaris L.) grown in crop rotations under different N content in Nicaragua. Secondary objectives were to estimate the fraction of
the measured soil mineral N content taken up in this way, and to determine how the measured N in plant aboveground parts was
related to the total mineral N uptake. A large variation in N content was obtained by using data from fertilisation experiments.
Plant total N uptake was estimated as the residual N in a mass balance calculation of soil mineral N. Mineral N content in
the top 0–0.3 m soil layer in the field cultivations and in tubes isolated from root uptake, and N content in aboveground
plant parts were measured every 30 days. Estimated plant total uptake of soil mineral N varied considerably (2.5–14 g N m−2 30 day−1) over periods and N treatments. The range of variation was similar for maize and bean. The fraction of the soil mineral N
that was taken up by the plant daily varied more in maize (about 0.03–0.12 day−1) than in bean (about 0.05–0.08 day−1). Our results suggest that monthly changes in N in aboveground plant parts were linearly related to plant total N uptake
during the same period. Aboveground plant N constituted between about 55% and 80% of total uptake of soil mineral N in maize
depending on period within season, whereas for bean it was more constant and smaller (about 40%). 相似文献
98.
Isidoro Izquierdo Cubero Maria T. Plaza Lopez-Espinosa Anthony C. Richardson 《Journal of chemical ecology》1993,19(6):1265-1283
The synthesis of (2S,5R)-(1) and (2R,5R)-2-methyl-1,6-dioxaspiro [4.5]decane (2) from (2RS,5R,8R,9R,10S)-8,9,10-trihydroxy-2-methyl-1, 6-dioxaspiro[4.5]decane (8), obtained in five steps fromd-fructose using Wittig's methodology, reduction, and spiroketalation, has been accomplished by a Corey dideoxygenation at C-8,9, followed by a Barton deoxygenation at C-10, of the appropriately protected derivatives.Enantiospecific synthesis of spirocetals. Part V. For Part IV, see Izquierdo et al. (1992). 相似文献
99.
Symmetries in constraint problems present an opportunity for reducing search. This paper presents Lightweight Dynamic Symmetry Breaking, an automatic symmetry breaking method that is efficient enough to be used as a default, since it never yields a major slowdown while often giving major performance improvements. This is achieved by automatically exploiting certain kinds of symmetry that are common, can be compactly represented, easily and efficiently processed, automatically detected, and lead to large reductions in search. Moreover, the method is easy to implement and integrate in any constraint system. Experimental results show the method is competitive with the best symmetry breaking methods without risking poor performance. 相似文献
100.
We analyze the complexity of equilibria problems for a class of strategic zero-sum games, called angel-daemon games. Those games were introduced to asses the performance of the execution of a web orchestration on a moderate faulty or under stress environment. Angel-daemon games are a natural example of zero-sum games whose representation is naturally succinct. We show that the problems of deciding the existence of a pure Nash equilibrium or of a dominant strategy for a given player are ${\Sigma}^{p}_{2}$ -complete. Furthermore, computing the value of an angel-daemon game is EXP-complete. Thus, our results match the already known classification of the corresponding problems for the generic families of succinctly represented games with exponential number of actions. 相似文献