全文获取类型
收费全文 | 2709篇 |
免费 | 41篇 |
国内免费 | 5篇 |
专业分类
电工技术 | 51篇 |
综合类 | 5篇 |
化学工业 | 214篇 |
金属工艺 | 9篇 |
机械仪表 | 40篇 |
建筑科学 | 106篇 |
矿业工程 | 1篇 |
能源动力 | 77篇 |
轻工业 | 54篇 |
水利工程 | 10篇 |
无线电 | 375篇 |
一般工业技术 | 255篇 |
冶金工业 | 1309篇 |
原子能技术 | 5篇 |
自动化技术 | 244篇 |
出版年
2022年 | 18篇 |
2021年 | 17篇 |
2020年 | 14篇 |
2019年 | 16篇 |
2018年 | 9篇 |
2017年 | 17篇 |
2016年 | 25篇 |
2015年 | 21篇 |
2014年 | 31篇 |
2013年 | 93篇 |
2012年 | 44篇 |
2011年 | 69篇 |
2010年 | 56篇 |
2009年 | 73篇 |
2008年 | 49篇 |
2007年 | 72篇 |
2006年 | 70篇 |
2005年 | 63篇 |
2004年 | 48篇 |
2003年 | 43篇 |
2002年 | 47篇 |
2001年 | 55篇 |
2000年 | 41篇 |
1999年 | 82篇 |
1998年 | 377篇 |
1997年 | 244篇 |
1996年 | 186篇 |
1995年 | 111篇 |
1994年 | 98篇 |
1993年 | 103篇 |
1992年 | 39篇 |
1991年 | 47篇 |
1990年 | 35篇 |
1989年 | 31篇 |
1988年 | 44篇 |
1987年 | 29篇 |
1986年 | 34篇 |
1985年 | 31篇 |
1984年 | 14篇 |
1983年 | 12篇 |
1982年 | 11篇 |
1981年 | 17篇 |
1980年 | 29篇 |
1979年 | 14篇 |
1978年 | 18篇 |
1977年 | 33篇 |
1976年 | 76篇 |
1975年 | 6篇 |
1973年 | 9篇 |
1972年 | 6篇 |
排序方式: 共有2755条查询结果,搜索用时 15 毫秒
21.
22.
Machining process planning involves the formation of a set of directions describing the machining operations required to transform raw stock into a finished part. Conventional process planning, performed manually, relies on the knowledge and competence of an experienced process planner and tends to be time consuming and error prone. In the past two decades, much effort has been spent on improving process planning by utilizing the power of a computer to emulate the capabilities of an experienced planner. During the same period, computer-aided design (CAD) and computer-aided manufacturing (CAM) software has been developed to enhance design productivity and to assist the NC code generation facets of the machining process. The entire planning process may be automated be integrating CAD and CAM using computer-aided process planing (CAPP). The research described in this paper outlines the design and development of an intelligent CAPP system integrating two commercial CAD and CAM software packages, Autocad and Mastercam. 相似文献
23.
JM Chow J Moncada D Brooks G Bolan H Shaw J Schachter 《Canadian Metallurgical Quarterly》1996,34(3):534-536
We evaluated the use of the leukocyte esterase test (LET) on first-catch urine specimens from women as a screening test to predict infection with Chlamydia trachomatis. For diagnosis, we used Abbott's ligase chain reaction (LCR) on urine specimens and isolation by tissue culture (TC) on cervical brushes. Of 4,053 women attending sexually transmitted disease and family planning clinics, 4.3% (n = 174) were positive by TC and 5.9% (n = 239) were positive by LCR. When LET was compared to TC, the sensitivity, specificity, positive predictive value, and negative predictive value were 54.0, 67.0, 6.8, and 97.0%, respectively. The corresponding performance of LET versus LCR was 53.1, 67.3, 10.1, and 95.8%. Almost half of the laboratory-confirmed chlamydial infections were negative by LET. The low specificity probably reflects multiple causes of pyuria in women and results in a low positive predictive value. LET is neither sensitive nor specific as a predictor of chlamydial infection and cannot be recommended for use as a screening test for C. trachomatis with first-catch urine samples from females from low- or moderate-prevalence populations. 相似文献
24.
PK Sanyal 《Canadian Metallurgical Quarterly》1993,17(4):325-331
Fenbendazole (Hoechst India Ltd.) was incorporated at 0.5 g/kg into urea molasses blocks made by two different processes. The proportion of the drug remaining in the blocks and the plasma concentrations of the parent compound and its metabolites were measured. Recovery of the drug in blocks made by the cold and the modified hot processes was 90% and 96%, respectively. The plasma metabolite profile revealed a plateau between days 4 and 6 of feeding in cattle and buffalo. However, the plasma concentrations of fenbendazole and its metabolites were low in buffalo compared to cattle. 相似文献
25.
The activity product of tetracalcium phosphate (TTCP, Ca4(PO4)2O), was determined at 37°C, and the hydrolysis of TTCP was investigated in 0.01–0.1 mol l–1 H3PO4 and KH2PO4 solutions by means of calcium and phosphorus analyses, X-ray diffraction and infrared analysis. The activity product, defined as K
sp=(Ca2+)4 (PO
4
3–
)2 (OH–)2, was 37.36 as pK
sp, which was smaller than that previously reported (42.4). TTCP easily hydrolysed to form calcium-deficient apatite (Ca-def OHAp, Ca5–x
(HPO4)
x
(PO4)3–x
(OH)1–x
), or dicalcium phosphate dihydrate (DCPD, CaHPO42H2O), depending on the initial phosphate concentration. With 0.1 mol l–1 H3PO4, TTCP hydrolysed to form DCPD within several minutes. In 0.025 mol l–1 H3PO4 and 0.1 mol l–1 KH2PO4, TTCP hydrolysed to form Ca-def OHAp through DCPD. In the latter solution, a small amount of octacalcium phosphate (OCP, Ca8(H2PO4)2(PO4)45H2O), was detected as an intermediate product. In 0.025 mol l–1 KH2PO4, TTCP hydrolysed directly to form Ca-def OHAp. In 0.01 mol l–1 H3PO4, hydrolysis of TTCP was not completed, although Ca-def OHAp was only a product. Thus the final product and the degree of hydrolysis depended on the pH and the overall Ca/P ratio in the reaction system. The rate of Ca-def OHAp formation seemed to be controlled by the dissolution rate of TTCP rather than the crystallization rate of the OHAp. 相似文献
26.
27.
28.
29.
K. Chatty T. P. Chow R. J. Gutmann E. Arnold D. Alok 《Journal of Electronic Materials》2002,31(5):356-360
Hall measurements have been used to compare the properties of 4H-SiC inversion-mode MOSFETs with “wet” and “dry” gate oxides.
While the field-effect mobilities were approximately 3–5 cm2/Vs, the Hall mobilities in 4H-SiC MOSFETs in the wet and dry oxide samples were approximately 70–80 cm2/Vs. The dry-oxidized metal oxide semiconductor field effect transistors (MOSFETs) had a higher transconductance, improved
threshold voltage, improved subthreshold slope, and a higher inversion carrier concentration compared to the wet-oxidized
MOSFETs. The difference in characteristics between the wet- and the dry-oxidized MOSFETs is attributed to the larger fixed
oxide charge in the dry oxide sample and a higher interface trap density in the wet oxide sample. 相似文献
30.
The authors study the performance of a multichannel modulation method for asymmetric digital subscriber lines (ADSLs) and very high-speed digital subscriber lines (VHDSLs). In the ADSL case, over all unloaded North American subscriber lines in the test set, a unidirectional 1.536 Mb/s data rate service from the end office to the customer premises is possible on a single twisted pair at an error rate of 10-7 with at least a 6 dB margin used coded multichannel modulation with sufficient transmit power. In the VHDSL case, data rates in excess of 100 Mb/s can be transmitted reliably, at an error rate of 10-7, using uncoded multichannel modulation on a single twisted pair over a distance ⩽150 ft with a sufficiently high sampling rate (≈24 MHz) and transmit power. It is shown that a cost-effective multichannel transceiver design suggested for high-speed digital subscriber line (HDSL) service will also work well for ADSL and VHDSL services with only minimal modifications 相似文献