全文获取类型
收费全文 | 710510篇 |
免费 | 10340篇 |
国内免费 | 2852篇 |
专业分类
电工技术 | 13700篇 |
技术理论 | 1篇 |
综合类 | 1702篇 |
化学工业 | 106696篇 |
金属工艺 | 28562篇 |
机械仪表 | 20942篇 |
建筑科学 | 18849篇 |
矿业工程 | 3102篇 |
能源动力 | 19225篇 |
轻工业 | 64564篇 |
水利工程 | 6724篇 |
石油天然气 | 11178篇 |
武器工业 | 114篇 |
无线电 | 82594篇 |
一般工业技术 | 133826篇 |
冶金工业 | 139096篇 |
原子能技术 | 13251篇 |
自动化技术 | 59576篇 |
出版年
2021年 | 6471篇 |
2020年 | 4692篇 |
2019年 | 5850篇 |
2018年 | 9638篇 |
2017年 | 9463篇 |
2016年 | 9880篇 |
2015年 | 7353篇 |
2014年 | 11868篇 |
2013年 | 32599篇 |
2012年 | 18919篇 |
2011年 | 26012篇 |
2010年 | 20746篇 |
2009年 | 23009篇 |
2008年 | 23944篇 |
2007年 | 23583篇 |
2006年 | 21021篇 |
2005年 | 19315篇 |
2004年 | 18262篇 |
2003年 | 18021篇 |
2002年 | 17439篇 |
2001年 | 17416篇 |
2000年 | 16172篇 |
1999年 | 17336篇 |
1998年 | 43795篇 |
1997年 | 30810篇 |
1996年 | 23808篇 |
1995年 | 17855篇 |
1994年 | 15520篇 |
1993年 | 15119篇 |
1992年 | 10906篇 |
1991年 | 10449篇 |
1990年 | 9909篇 |
1989年 | 9631篇 |
1988年 | 9102篇 |
1987年 | 7928篇 |
1986年 | 7853篇 |
1985年 | 8900篇 |
1984年 | 8293篇 |
1983年 | 7332篇 |
1982年 | 6906篇 |
1981年 | 7020篇 |
1980年 | 6640篇 |
1979年 | 6393篇 |
1978年 | 6167篇 |
1977年 | 7603篇 |
1976年 | 10380篇 |
1975年 | 5368篇 |
1974年 | 5036篇 |
1973年 | 5135篇 |
1972年 | 4229篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
231.
M Kanazawa M Yano C Namchai S Yamamoto A Ohtake M Takayanagi M Mori H Niimi 《Canadian Metallurgical Quarterly》1997,239(2):580-584
cDNAs for green fluorescent protein (GFP) and for a GFP fusion protein containing the presequence of human ornithine transcarbamylase (pOTC-GFP) were transfected into cultured human fibroblasts. GFP cDNA gave diffuse fluorescence throughout the cytoplasm and the nucleus, whereas pOTC-GFP cDNA gave mitochondria-associated fluorescence. Fluorescent mitochondrial structures could be classified into five patterns: thread-like mitochondria, fine thread-like ones, rod-like ones, granular ones, and granular ones with weak cytosolic fluorescence. pOTC-GFP mutants resulted in a loss of mitochondrial fluorescence and an appearance of weak fluorescence throughout the cytoplasm. pOTC-GFP cDNA was transfected into fibroblasts from patients with various mitochondrial diseases. Higher ratios of fibroblasts with granular mitochondria and those with fine thread-like ones were observed in a patient with Reye's syndrome and a patient with Kearns-Sayre syndrome. Weak cytosolic fluorescence was sometimes observed in fibroblasts from these patients. This method will be useful to analyze mitochondrial structural alterations and disorders of mitochondrial protein import. 相似文献
232.
233.
ME Sutherlin I Nishimori T Caffrey EP Bennett H Hassan U Mandel D Mack T Iwamura H Clausen MA Hollingsworth 《Canadian Metallurgical Quarterly》1997,57(21):4744-4748
The levels of mRNA expression of three UDP-N-acetyl-alpha-D-galactosamine:polypeptide GalNAc N-acetylgalactosaminyltransferases (GalNAc-transferases) were quantified for human adenocarcinoma cell lines from pancreas, colon, stomach, and breast. Two of the GalNAc-transferases, GalNAc-T1 and GalNAc-T2, were expressed constitutively and at low levels in most or all cell lines examined. A third GalNAc-transferase, GalNAc-T3, was differentially expressed. Well-differentiated adenocarcinoma cell lines expressed high levels and moderately differentiated cell lines expressed lower levels of GalNAc-T3. Cell lines classified as poorly differentiated failed to express GalNAc-T3 mRNA at levels that could be detected by Northern blot analysis. Differential expression of the GalNAc-T3 protein was confirmed in these cell lines by Western blotting. We propose that glycosylation in tumor cell lines may be regulated in part by differential expression of GalNAc-transferases, and we suggest that GalNAc-T3 gene expression may be a molecular indicator of differentiated adenocarcinoma. 相似文献
234.
Cresswell M.W. Allen R.A. Guthrie W.F. Sniegowski J.J. Ghoshtagore R.N. Linholm L.W. 《Semiconductor Manufacturing, IEEE Transactions on》1998,11(2):182-193
The physical widths of reference features incorporated into electrical linewidth test structures patterned in films of monocrystalline silicon have been determined from Kelvin voltage measurements. The films in which the test structures are patterned are electrically insulated from the bulk-silicon substrate by a layer of silicon dioxide provided by SIMOX (Separation by the IMplantation of OXygen) processing. The motivation is to facilitate the development of linewidth reference materials for critical-dimension (CD) metrology-instrument calibration. The selection of the (110) orientation of the starting silicon and the orientation of the structures' features relative to the crystal lattice enable a lattice-plane-selective etch to generate reference-feature properties of rectangular cross section and atomically planar sidewalls. These properties are highly desirable for CD applications in which feature widths are certified with nanometer-level uncertainty for use by a diverse range of CD instruments. End applications include the development and calibration of new generations of CD instruments directed at controlling processes for manufacturing devices having sub-quarter-micrometer features 相似文献
235.
P Virsik-Peuckert M Rave-Fr?nk U Langebrake H Schmidberger 《Canadian Metallurgical Quarterly》1997,148(3):209-215
The modulatory role of locally produced cyclooxygenase products and endothelium-derived nitric oxide in controlling vascular tone was investigated in bovine intra-mammary artery. Vascular reactivity initiated by vasoactive compounds, endothelin-1 (ET-1), bradykinin (BK), and substance P (SP) was measured isometrically in an isolated tissue bath. The effects of a cyclooxygenase inhibitor, indomethacin (10(-5) M) and an inhibitor of nitric oxide production, N omega-Nitro L-Arginine (L-NNA: 3 x 10(-4) M) were determined during agonist-mediated responses. Indomethacin alone markedly enhanced vascular contraction produced by ET-1, while L-NNA did not. Inhibition of endothelium-derived nitric oxide synthesis by L-NNA, however, significantly attenuated BK- and SP-induced vascular relaxations, whereas indomethacin had slight influence. The potentiation between indomethacin and L-NNA in regulating vasomotor tone was not observed in this vascular bed. Thus, it appeared that both the cyclooxygenase and endothelium-derived nitric oxide pathways participated in modifying vascular reactivity. Domination of one pathway over the other depended upon the agonist used to stimulate vascular tissue. 相似文献
236.
A new commercially available diode model is described. This unified model is capable of simulating the widest range of diode technologies of any presently available. The emphasis of this paper is on describing the model's extensive features and flexibility in the different domains of operation and is of particular interest in power applications 相似文献
237.
JC Métraux 《Canadian Metallurgical Quarterly》1997,117(5):419-423
The purpose of this study was to assess cortical and cancellous bone responses to unilateral limb immobilization and, subsequently, to remobilization with exercise, in a young adult canine model. Right forelimbs of 14 1-2-year old mongrel dogs were immobilized in a non-weight-bearing position by a bandage for 16 weeks. Six control dogs were untreated. At 16 weeks, seven immobilized and three control dogs were euthanized. The remaining seven immobilized dogs began a recovery protocol consisting of 16 weeks of kennel confinement (without the right forelimb bandaged) followed by 16 weeks of treadmill exercise conducted three times per week. These seven dogs and three control dogs were euthanized at 48 weeks. Bone mineral density of the proximal radii was determined with dual-energy X-ray absorptiometry and humeral middiaphyseal cross-sectional areas were determined with computed tomography. Humeri were tested in cranio-caudal three-point bending to failure. Cancellous bone cores from the lateral humeral condyles had wet apparent density determined and were tested to failure in compression. Mechanical properties, bone density, and cross-sectional areas were compared between immobilized (right forelimb), contralateral weight bearing (left forelimb), and control forelimbs with Kruskal-Wallis and post hoc tests. At 16 weeks, bone mineral density, cortical load, yield, and stiffness as well as cancellous bone failure stress, yield stress, and modulus were significantly lower (p < 0.02) for immobilized limbs than control limbs. Immobilized limb cancellous bone mechanical properties were 28%-74% of control values, and cortical bone mechanical properties were 71%-98% of control values. After 32 weeks of remobilization, cortical and cancellous bone mechanical properties were not different from control values except that cortical bone failure stress and modulus were significantly higher (p < 0.01) between remobilized and control limbs. In summary, 16 weeks of forelimb immobilization was associated with significantly lower mechanical properties, and with greater differences in cancellous than cortical bone properties. Mechanical properties were not different from control values after 32 weeks of recovery that included 16 weeks of treadmill exercise. 相似文献
238.
Photonic networks based on the optical path concept and wavelength division multiplexing (WDM) technology require unique operation, administration, and maintenance (OAM) functions. In order to realize the required OAM functions, the optical path network must support an effective management information transfer method. The method that superimposes a pilot tone on the optical signal appears very interesting for optical path overhead transfer. The pilot tone transmission capacity is determined by the carrier to noise ratio which depends on the power spectral density of the optical signal. The pilot tone transmission capacity of an optical path network employing WDM technology is elucidated; 4.5 kb/s transmission can be realized when the pilot tone modulation index is set at 3% 相似文献
239.
In order to observe the transport ability of peritoneum to small molecular substances, peritoneal equilibration test (PET) was performed in 52 CAPD patients. By analysing the relationship between peritoneal transport function and dialysis adequacy, we found the average urea KT/V and Cr were significantly lower in high and low transport groups (n = 6 and n = 2) than in high average and low average groups (n = 35 and n = 9). According to the results of PET, we adjusted the dialysis program of 11 patients and the dialysis adequacy was markedly improved. We concluded that PET was helpful for selecting and adjusting CAPD program, and discussed some questions which should be payed more attention in PET operation. 相似文献
240.
John C. Hart Gordon W. Lescinsky Daniel J. Sandin Thomas A. DeFanti Louis H. Kauffman 《The Visual computer》1993,9(7):346-355
The pipelined architecture and parallel organization of the AT&T Pixel Machine image computer are described and demonstrated with applications for the visualization of multidimensional fractals, particularly linear fractals and quaternion/ stacked Julia sets. Techniques for pushing the Pixel Machine to its peak abilities are described and apply to more recent parallel image computers as well. 相似文献