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101.
A series of polyesters was prepared to evaluate hydrolytic stability as a function of cyclohexyl dibasic acid content. The
three cyclohexyl dibasic acids: 1,2; 1,3; and 1,4 were formulated into polyesters with two glycols. The proportion of cis
and trans isomers was evaluated via 1H NMR. The hydrolytic stability of short chain polyesters was evaluated in an acetone/water mixture which solubilized the
polyesters to mimic oligoester behavior within a thermosetting polyester coating environment. The rate of hydrolysis was monitored
by acid titration and corroborated by GPC. Surprisingly, 1,2-cylohexyl diacid-based polyesters were robust, and 1,3-cyclohexyl
diacid-based polyesters were the most susceptible to hydrolysis. Evidently, a 1,2-anchimeric effect for cyclohexyl dibasic
acid polyesters was not an important consideration, while the 1,3-cyclohexyl ester interaction was. Consequently, an anomeric
effect was proposed.
Presented at the 81st Annual Meeting of the Federation of Societies for Coatings Technology, November 12–14, 2003, in Philadelphia,
PA. 相似文献
102.
J. Johnson 《Artificial Life and Robotics》2003,7(1-2):16-21
Popular interest in robotics has increased astonishingly in the last few years. Robotics is seen by many as offering major new benefits in education at all levels. Before rushing to exploit this popularity, educators should ask serious questions about the universality and longevity of the robotics phenomenon. Is it a fashion? To be useful, the energy released by robotics must be sustained and universal, and the means of exploiting it must be systematic. Universities define their own robotics curriculum, but most schools lack both the resources and the freedom to do this, and must work with a national curriculum. If it can be shown that robotics has sustained potential in education, it seems inevitable that new ways need to be found to integrate it into the school curriculum. 相似文献
103.
F. G. Johnson B. L. Olmsted Samuel Chen G. W. Wicks 《Journal of Electronic Materials》1993,22(3):331-334
The composition profile of an (AlAs)1/2(GaAs)1/2 tilted superlattice is characterized for the first time. The tilted superlattice sample is thermally disordered, and the
energy of the direct band gap photoluminescence peak is measured as a function of increasing layer interdiffusion. The shift
in the photoluminescence peak energy after completely disordering the tilted superlattice is 39 meV. A theoretical model is
used to simulate the change in band gap as a function of layer interdiffusion for several composition profiles. The profile
that gives the best fit to the experimental data is chosen. The tilted superlattice composition profile is found to be sinusoidal,
varying from Al0.40Ga0.60As to Al0.60Ga0.40As. 相似文献
104.
105.
M. E. özsan D. R. Johnson M. Sadeghi D. Sivapathasundaram G. Goodlet M. J. Furlong L. M. Peter A. A. Shingleton 《Journal of Materials Science: Materials in Electronics》1996,7(2):119-125
Thin CdS films have been grown by chemical bath (CdCl2, thiourea, ammonia) deposition (CBD) on SnO2 (TO)-coated glass substrate for use as window materials in CdS/CdTe solar cells. High-resolution transmission electron microscopy revealed grains with an average size of 10 nm. The structure was predominantly hexagonal with a high density of stacking faults. The film crystallinity improved with annealing in air. Annealing in a CdCl2 flux increased the grain size considerably and reduced the density of stacking faults. The optical transmission of the as-deposited films indicated a band gap energy of 2.41 eV. Annealing in air reduced the band gap by 0.1 eV. Annealing in CdCl2 led to a sharper optical absorption edge that remained at 2.41 eV. Similar band gap values were obtained by photocurrent spectroscopy and electroabsorption spectroscopy (EEA) using an electrolyte contact. EEA spectra were broad for the as-deposited and air-annealed samples, but narrower for the CdCl2-annealed films, reflecting the reduction in stacking fault density. Donor densities of ca. 1017 cm –3 were derived from the film/electrolyte junction capacitance. 相似文献
106.
M Knoepfelmacher MJ Pradal RD Dio LR Salgado M Semer BL Wajchenberg B Liberman 《Canadian Metallurgical Quarterly》1997,137(2):162-166
OBJECTIVE: To assess the plasma levels and action of arginine vasopressin (AVP) in patients with Cushing's disease. There are many reports that patients with Addison's disease have increased AVP levels associated with hyponatraemia and hypoosmolality, but none on the dynamics of secretion of this neurohormone during osmolality-based stimulation in patients with chronic hypercortisolism. DESIGN AND SUBJECTS: The plasma AVP concentration and the urinary and plasma osmolality after a 7.5-h water deprivation test (WDT) were evaluated in 13 patients with Cushing's disease and 15 normal (control) individuals. In patients with Cushing's disease we also assessed the urinary osmolality in response to 10 micrograms i.v. desmopressin (DDAVP) administered at the end of the WDT. RESULTS: At the end of the WDT, urinary osmolality was significantly lower in patients with Cushing's disease (511.5 +/- 148.5 mOsm/l) than in the normal subjects (981.1 +/- 107.1 mOsm/l, P < 0.001), whereas plasma osmolality did not differ between the two groups. Consequently, the urine/plasma osmolality ratio (Uosm/Posm) was lower in patients with Cushing's disease than in normal individuals (1.8 +/- 0.5 compared with 3.4 +/- 0.4, P < 0.001). The AVP concentration also was greater (7.3 +/- 3.1 pmol/l) in those with Cushing's disease than in the controls (3.9 +/- 2.3 pmol/l, P < 0.005). After administration of DDAVP to the hypercortisolaemic patients, the urinary osmolality attained (718.0 +/- 200.0 mOsm/l) was still lower than that in the normal group at the end of WDT (P < 0.005). CONCLUSIONS: Patients with Cushing's disease presented higher AVP levels and smaller Uosm/Posm ratios than normal subjects. After DDAVP, the patients with Cushing's disease were unable to concentrate the urine adequately. These data suggest that the kidney shows resistance to the action of both endogenous and exogenous AVP in patients with Cushing's disease. 相似文献
107.
Johnson R.A. de la Houssaye P.R. Chang C.E. Pin-Fan Chen Wood M.E. Garcia G.A. Lagnado I. Asbeck P.M. 《Electron Devices, IEEE Transactions on》1998,45(5):1047-1054
This paper reviews the prospects of thin-film silicon-on-sapphire (TFSOS) CMOS technology in microwave applications in the 1-5 GHz regime and beyond and presents the first demonstration of microwave integrated circuits based on this technology, MOSFET's optimized for microwave use, with 0.5-μm optically defined gate lengths and a T-gate structure, have ft values of 25 GHz (14 GHz) and fmax values of 66 GHz (41 GHz) for n-channel (p-channel) devices and have noise figure values below 1 db at 2 GHz, some of the best reported performance characteristics of any silicon-based MOSFET's to date. On-chip spiral inductors exhibit quality factors above ten. Circuit performance compares favorably with that of other CMOS-based technologies and approach performance levels similar to those obtained by silicon bipolar technologies. The results demonstrate the significant potential of this technology for microwave applications 相似文献
108.
HM Trist SG Tyack MA Johnson CT Prideaux M Sheppard 《Canadian Metallurgical Quarterly》1996,40(1):130-139
Restriction enzyme linkage maps were produced for the genomic short region of the virulent infectious laryngotracheitis virus (CSW-1 strain). After comparison with the equivalent restriction enzyme linkage maps for the infectious laryngotracheitis virus SA-2 strain (a vaccine strain), it was determined that the maps for the short regions of the two strains were identical, apart from a single section in each of the inverted terminal repeats. Each inverted terminal repeat of the SA-2 strain was discovered to contain 467 base pairs more DNA than the CSW-1 strain's inverted terminal repeats. This extra DNA was more precisely mapped entirely within the EcoRI fragments D and d of SA-2, which were found to form part of the SmaI fragments U and P of SA-2 and Q and b of SA-2 and to contain one SmaI restriction enzyme site. 相似文献
109.
Despite the fact that the neuroleptic drugs have been widely used for more than 40 years, one of their most common side-effects, akathisia, has been relatively neglected. There are still no universally agreed diagnostic criteria for akathisia, particularly chronic akathisia, and in this review article, we discuss the controversies surrounding the voluntary nature of its motor features and the importance of the dysphoric component. We also review the published epidemiological studies to show the great variation in frequency of occurrence. Finally, we discuss the possible neurotransmitters involved in the pathophysiology and treatment of this condition. 相似文献
110.
CB McCoy SA Smith LR Metsch RS Anwyl R Correa L Bankston JJ Zavertnik 《Canadian Metallurgical Quarterly》1994,2(4):267-274
Socioeconomic status is the most significant factor influencing the decreased survival associated with breast cancer in minority groups in the United States. Barriers to the use of early detection programs by low-income women often result in the detection of breast cancer at stages too advanced to assure optimum outcomes. In an effort to increase accessibility of breast cancer screening among such individuals, the Early Detection Program (EDP) was initiated in 1987. The program provided breast cancer screening to women 40 years of age and older who attended eight primary healthcare centers located in low-income neighborhoods throughout Dade County, Florida. From its inception in October 1987 through December 1993, 23,866 medically underserved women had mammography examinations, with more than 17,000 of these women undergoing baseline mammograms. Since the program's inception, 126 cancers were diagnosed in 123 women. A dramatic shift from later to earlier stage breast cancers was observed. These results warrant a greater inclusion of medically underserved and lower socioeconomic status women in screening programs for the early detection of breast cancer. 相似文献