全文获取类型
收费全文 | 57503篇 |
免费 | 6697篇 |
国内免费 | 4011篇 |
专业分类
电工技术 | 5187篇 |
技术理论 | 2篇 |
综合类 | 4592篇 |
化学工业 | 8188篇 |
金属工艺 | 3174篇 |
机械仪表 | 3839篇 |
建筑科学 | 4486篇 |
矿业工程 | 1948篇 |
能源动力 | 1744篇 |
轻工业 | 4793篇 |
水利工程 | 1502篇 |
石油天然气 | 2638篇 |
武器工业 | 775篇 |
无线电 | 7267篇 |
一般工业技术 | 5996篇 |
冶金工业 | 2036篇 |
原子能技术 | 850篇 |
自动化技术 | 9194篇 |
出版年
2024年 | 331篇 |
2023年 | 1012篇 |
2022年 | 2063篇 |
2021年 | 2984篇 |
2020年 | 2138篇 |
2019年 | 1697篇 |
2018年 | 1917篇 |
2017年 | 2177篇 |
2016年 | 2044篇 |
2015年 | 2861篇 |
2014年 | 3539篇 |
2013年 | 4296篇 |
2012年 | 4869篇 |
2011年 | 4918篇 |
2010年 | 4493篇 |
2009年 | 4228篇 |
2008年 | 3954篇 |
2007年 | 3749篇 |
2006年 | 3358篇 |
2005年 | 2606篇 |
2004年 | 1854篇 |
2003年 | 1338篇 |
2002年 | 1300篇 |
2001年 | 1023篇 |
2000年 | 768篇 |
1999年 | 536篇 |
1998年 | 336篇 |
1997年 | 268篇 |
1996年 | 253篇 |
1995年 | 226篇 |
1994年 | 163篇 |
1993年 | 101篇 |
1992年 | 96篇 |
1991年 | 69篇 |
1990年 | 57篇 |
1989年 | 46篇 |
1988年 | 32篇 |
1987年 | 28篇 |
1986年 | 31篇 |
1985年 | 35篇 |
1984年 | 42篇 |
1983年 | 31篇 |
1982年 | 32篇 |
1981年 | 31篇 |
1980年 | 35篇 |
1979年 | 28篇 |
1978年 | 20篇 |
1977年 | 27篇 |
1976年 | 34篇 |
1975年 | 21篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
91.
汪波 《单片机与嵌入式系统应用》2012,12(2):22-24,28
以AVR单片机ATmega48芯片及CMX865调制/解调芯片为硬件架构规范了对外串口通信协议,采用模拟口线的方式对CMX865寄存器进行操作,设计了一种串口转FSK的通信模块,实现数据传输方式的转换。硬件电路以AT—mega48微处理器为核心,并利用C/BUS总线控制CMX865芯片,实现FSK/DTMF收、发功能;... 相似文献
92.
Non-homogeneity detector (NHD) is known for improving the detection performance of space time adaptive processing (STAP) in heterogeneous environment. To mitigate the finite sample effect in the generalized inner product (GIP) based NHD, a new type of GIP detector based on diagonal loading (LGIP) is proposed in this paper. We derive the theoretical mean value of LGIP detector based on random matrix theory. Moreover, an approximation of the theoretical mean value is provided for practical considerations. We then apply the derived theoretical mean value of LGIP to the detection of heterogeneous samples. Finally, by theoretical analysis and numerical simulations, we show the effectiveness of the proposed detector. 相似文献
93.
In this article, the influence of base resistance on extracting thermal resistance for SiGe heterojunction bipolar transistors is studied and an improved approach for determining the junction temperature and thermal resistance is presented. The proposed method for extracting thermal resistance is based on the temperature sensitivity of the base–emitter (B–E) voltage when the device is biased with a fixed emitter current density. This approach not only takes into account the self‐heating during the different ambient temperature measurement but also revises the empirical equation of B–E voltage due to the influence of base resistance during the power dissipation increment measurement. Results are obtained for devices with different emitter lengths and fingers. Compared with the conventional method, the thermal resistance is about up to 15% improvement for the device with 0.3 × 1.9 μm2 emitter area and 13.8% for the device with 0.3 × 13.9 μm2 emitter area. The accurate thermal resistance implemented in HICUM model has resulted in better fit for transistor output characteristics. © 2012 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2012. 相似文献
94.
Wei-Lan Suo Bo Feng Zhi-Ping Fan 《Soft Computing - A Fusion of Foundations, Methodologies and Applications》2012,16(3):471-483
The decision making trial and evaluation laboratory (DEMATEL) method is a useful tool for analyzing correlations among factors
using crisp values. However, the crisp values are inadequate to model real-life situations due to the fuzziness and uncertainty
that are frequently involved in judgments of experts. The aim of this paper is to extend the DEMATEL method to an uncertain
linguistic environment. In this paper, the correlation information among factors provided by experts is in the form of uncertain
linguistic terms. A formula is first presented to transform correlation information from uncertain linguistic terms to trapezoidal
fuzzy numbers. Then, we aggregate the transformed correlation information of each expert into group information using the
operations of trapezoidal fuzzy numbers. The importance and classification of factors are determined via fuzzy matrix operations.
Furthermore, a causal diagram is constructed to vividly show the different roles of factors. Finally, an example is used to
illustrate the procedure of the proposed method. 相似文献
95.
There is a large body of evidence indicating that activities associated with regrouping of bulls before slaughter, which leads to physical exhaustion mainly from mounting, are primary factors inducing dark-cutting (DFD) in beef. The aim of this study was to test several methods to control activity when regrouping cannot be avoided. Fifty bulls previously individually tied for at least 16 months were drafted into groups of five animals and released in a pen at the abattoir. After 18 to 22 h they were slaughtered. According to environmental conditions in the pen, the bulls were divided into four groups: Control group (n = 10, no experimentation); Electricity group (n = 10, an electric fence was constructed above the pen so that a mounting bull would receive an electric shock); Darkness group (n = 10, the whole stall was in darkness); and Combination group (n = 20, both treatments, of the electricity and darkness groups were applied). During the first hour of penning the behaviour of the bulls was videorecorded. After slaughter meat quality characteristics were measured. Dark-cutting was found in Control (70%), Electricity (30%) and Darkness (70%) groups, but not in the Combination group (0%). No treatment altered the repertoire of agonistic activity, but under the combined treatments the number of agonistic interactions was significantly lower than in any other group. 相似文献
96.
本文按照维氏硬度测定的技术条件,将基本公式H_v=1854P/D~2加以变换,从而得到一些较为简单的数学关系式.利用这些关系式,可以对不同金属薄带材料,很容易计算出较合理的负荷大小,既能保证不被"打穿",也使视场内有一个适合观测的压痕图象. 相似文献
97.
T. Lalinsky J. Kuzmík D. Gregušová Ž. Mozolová J. Breza M. Feciško P. Seidl 《Journal of Materials Science: Materials in Electronics》1992,3(3):157-161
The formation of WN
x
/GaAs Schottky contacts using selective ion implantation of nitrogen into the sputtered tungsten film has been demonstrated. The contacts were characterized by Auger electron spectroscopy and current-voltage measurements. The composition of WN
x
films and the thermal stability of WN
x
/GaAs contacts were investigated. Good thermal stability of WN
x
/GaAs contacts compared with a W/GaAs contact was observed after capless rapid thermal annealing at 450, 800 and 950°C for 10 s. 相似文献
98.
Kosta Došen 《Journal of Logic, Language and Information》1992,1(3):173-201
The goal of this paper is to show how modal logic may be conceived as recording the derived rules of a logical system in the system itself. This conception of modal logic was propounded by Dana Scott in the early seventies. Here, similar ideas are pursued in a context less classical than Scott's.First a family of propositional logical systems is considered, which is obtained by gradually adding structural rules to a variant of the nonassociative Lambek calculus. In this family one finds systems that correspond to the associative Lambek calculus, linear logic, relevant logics, BCK logic and intuitionistic logic. Above these basic systems, sequent systems parallel to the basic systems are constructed, which formalize various notions of derived rules for the basic systems. The deduction theorem is provable for the basic systems if, and only if, they are at least as strong as systems corresponding to linear logic, or BCK logic, depending on the language, and their deductive metalogic is not stronger than they are.However, though we do not always have the deduction theorem, we may always obtain a modal analogue of the deduction theorem for conservative modal extensions of the basic systems. Modal postulates which are necessary and sufficient for that are postulates of S4 plus modal postulates which mimic structural rules. For example, the modal postulates which Girard has recently considered in linear logic are necessary and sufficient for the modal analogue of the deduction theorem.All this may lead towards results about functional completeness in categories. When functional completeness, which is analogous to the deduction theorem, fails, we may perhaps envisage a modal analogue of functional completeness in a modal category, of which our original category is a full subcategory. 相似文献
99.
针对新时代环境下Newsvendor型产品销售期短、期末未出售产品价值递减的产品特点,生产链要求位于上游的供应商必须快速加工出所需的工件,否则将面临着线性递增的拖期惩罚。在面对基于Newsvendor型产品的柔性作业车间调度问题时,设计了一种加入禁忌搜索的混合遗传算法,扩大了解的搜索范围,避免了传统遗传算法容易陷于局部最优的缺陷。最后利用混合遗传算法对一个仿真案例进行求解。 相似文献
100.