全文获取类型
收费全文 | 1589篇 |
免费 | 84篇 |
国内免费 | 1篇 |
专业分类
电工技术 | 14篇 |
综合类 | 1篇 |
化学工业 | 337篇 |
金属工艺 | 39篇 |
机械仪表 | 34篇 |
建筑科学 | 47篇 |
矿业工程 | 4篇 |
能源动力 | 64篇 |
轻工业 | 100篇 |
水利工程 | 8篇 |
石油天然气 | 4篇 |
无线电 | 163篇 |
一般工业技术 | 294篇 |
冶金工业 | 275篇 |
原子能技术 | 18篇 |
自动化技术 | 272篇 |
出版年
2024年 | 4篇 |
2023年 | 19篇 |
2022年 | 39篇 |
2021年 | 55篇 |
2020年 | 27篇 |
2019年 | 46篇 |
2018年 | 48篇 |
2017年 | 35篇 |
2016年 | 51篇 |
2015年 | 49篇 |
2014年 | 62篇 |
2013年 | 105篇 |
2012年 | 94篇 |
2011年 | 147篇 |
2010年 | 85篇 |
2009年 | 87篇 |
2008年 | 93篇 |
2007年 | 63篇 |
2006年 | 67篇 |
2005年 | 48篇 |
2004年 | 31篇 |
2003年 | 31篇 |
2002年 | 18篇 |
2001年 | 10篇 |
2000年 | 12篇 |
1999年 | 16篇 |
1998年 | 57篇 |
1997年 | 45篇 |
1996年 | 28篇 |
1995年 | 20篇 |
1994年 | 14篇 |
1993年 | 16篇 |
1992年 | 9篇 |
1991年 | 14篇 |
1990年 | 11篇 |
1989年 | 11篇 |
1988年 | 9篇 |
1987年 | 4篇 |
1986年 | 5篇 |
1985年 | 9篇 |
1984年 | 5篇 |
1983年 | 7篇 |
1982年 | 7篇 |
1980年 | 9篇 |
1979年 | 5篇 |
1978年 | 4篇 |
1977年 | 10篇 |
1976年 | 5篇 |
1975年 | 4篇 |
1954年 | 3篇 |
排序方式: 共有1674条查询结果,搜索用时 46 毫秒
1.
2.
Maria A. Ospina Monica Pizarro Thierry Tran Julien Ricci John Belalcazar Jorge L. Luna Luis F. Londoño Sandra Salazar Hernan Ceballos Dominique Dufour Luis A. Becerra Lopez-Lavalle 《International Journal of Food Science & Technology》2021,56(3):1343-1353
The objective of this study was to characterise the nutritional potential of leaves and identify a diversity centre with low cyanide and high nutrient content among 178 Latin American cassava genotypes. This field-based collection represents the seven diversity centres, held at The International Center for Tropical Agriculture (CIAT Palmira, Colombia) by the Cassava Program. The cyanide, all-trans-β-carotene and lutein concentrations in cassava leaves ranged from 346 to 7484 ppm dry basis (db), from 174–547 μg g−1 db and 15–181 μg g−1 db, respectively. Cassava leaves also showed significant levels of essential amino acids leucine, lysine, phenylalanine, valine and threonine, and average total protein content of 26.24 g 100 g−1 db. Among seven diversity centres, South American rainforest group showed low cyanide and high carotene content in leaves. In addition, VEN77 and PAN51 genotypes stood out for having low cyanide in leaves and roots and high carotene in leaves. This genetic diversity can be used to select high potential progenitors for breeding purposes. 相似文献
3.
Various image processing applications exploit a model of the human visual system (HVS). One element of HVS-models describes the masking-effect, which is typically parameterized by psycho-visual experiments that employ superimposed sinusoidal stimuli. Those stimuli are oversimplified with respect to real images and can capture only very elementary masking-effects. To overcome these limitations a new psycho-visual test method is proposed. It is based on natural scenery stimuli and operates in the wavelet domain. The collected psycho-visual data is finally used to evaluate the performance of various masking models under conditions as found in real image processing applications like compression. 相似文献
4.
The hydrodynamic impact problem is investigated within the framework of potential-flow theory. The vertical load acting on the rigid body is derived based on either momentum or energy conservation, and using the concept of added mass together with a homogeneous Dirichlet condition for the potential on the free surface as usually done to model an impact problem. It is demonstrated that the use of this simplified dynamic free-surface condition, instead of the fully nonlinear one, has a direct influence on the computation of the loads. In particular, the equivalence of momentum and energy analysis is in general not recovered. The situation is then highlighted by performing an asymptotic analysis of the two-dimensional blunt-body asymmetric impact problem. The asymptotic solution is given explicitly and validated through comparisons with experimental results. The energy distribution is then studied. It is shown that the contradiction between momentum and energy analysis can be removed, provided that the flux of energy through the jets is taken into account in the energy balance. If the simplified free-surface condition is indeed valid in the far-field, nonlinear terms must be retained near the body, in the spray-root domains. To leading order, the energy distribution during the gravity-free inertia stage does not depend on the blunt-body shape. The general analysis based on momentum or energy conservation suggests that this result also applies for arbitrary body shape as soon as a homogeneous Dirichlet condition can be applied as a dynamical free-surface boundary condition. In this case, and for a constant vertical impact velocity, half the work performed by the body would seem to be transferred to the fluid as kinetic energy within the spray. 相似文献
5.
We study the effect of Josephson coupling between adjacent superconducting layers on the BCS energy spectrum. We find that the interference between the gap functions of two layers can lead to vanishing condensation energy for perpendicular momenta corresponding to the formation of standing waves. We therefore predict a conventional energy spectrum for large interlayer spacings, if the gap of the single layers has no nodes, and in all cases a gapless spectrum for small spacings. Within the experimental error, our numerical results account for the low-temperature dependence of the penetration depth reported in Nd1.85Ce0.15CuO4 and YBa2Cu3O6.9. 相似文献
6.
Jean-Louis Iehl Rodolphe Grac Luc le Gratiet Véronique Bardinal Rainer Buhleier Elena Bedel-Pereira Chantal Fontaine Michel Pugnet Jacques-Henry Collet 《电信纪事》1997,52(11-12):627-637
We study the transient gratings photogenerated in the picosecond regime in three families of structures, namely : - structures of thickness in the order of one micron, including quantum wells (GaAs/GaAlAs, CdTe/ CdZnTe). A transmission modulation due to the electric field has been observed. We show that, in accordance with our calculations, this modulation is screened faster than 10 ps at a fluence of a few µJ/cm2. - A structure including GalnAs/GalnAsP MQWS in a cavity. This structure shows a top diffraction efficiency of 2.5 × 10-2 at 1.55 µm for an energy of excitation in the order of 100 µJ/cm2. The diffraction efficiency exhibits several oscillations due to Fabry-Pårot effects. By introducing cavity effects in our model, we show that the diffraction efficiency is amplified by more than a factor 2 with respect to the no-cavity case. Calculations show that the diffraction efficiency may reach 6 × 10-2 around 1.625 µm, for a front mirror reflectivity of 90 %. - Structures including bulk GaAs microcavities. The risetime is lower or in the order of 1 ps while the diffraction efficiency attains 1 %, with an average power of 4 mW (i.e. an energy of 2 µJ/cm2/pulse), compatible with a commutation of packets at 80 MHz. 相似文献
7.
The reactivity of lithium with layered chalcogenides InSe and In2Se3 is studied using transmission electron microscopy (TEM), electrochemical potential spectroscopy (EPS) and Raman scattering (RS). It is found that for x(Li)≥0.1 in LixInSe, the host material decomposes with the formation of lithium selenide. The presence of Li2Se is confirmed by Raman spectroscopy. The insertion of Li into In2Se3 appears more stable with the occurrence of a superlattice formation at x(Li)≈0.25. The superstructure corresponding to the 2a×2a lattice is consistent with the EPS measurements of LixIn2Se3. 相似文献
8.
Faith Myles S.; Fontaine Kevin R.; Baskin Monica L.; Allison David B. 《Canadian Metallurgical Quarterly》2007,133(2):205
The authors reviewed the evidential basis of three environmental approaches to reducing population obesity: What are the effects of (a) taxing or subsidizing foods, (b) manipulating the ease of food access, and (c) restricting access to certain foods? A narrative review evaluated evidence using National Heart, Lung, and Blood Institute criteria. There was strong evidence that subsidization influences food purchases, but not necessarily food consumption or body weight. Ease of food access may influence food purchases, and possibly food intake and body weight. Data on restriction were lacking. More studies are needed to justify that altering these macro-environmental variables will necessarily reduce population obesity. A proposed conceptual model posits that the steps through environmental interventions may exert intended and unintended influences on body weight and obesity prevalence. Contemplated policy changes should weigh scientific evidence with social judgments and values concerning changes to the environment. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
9.
PURPOSE: Retrospective evaluation of the efficacy of percutaneous nephrostomy and nephroureteral stent placement for treatment of post-transplant ureteral leak, and percutaneous nephrostomy and balloon dilation for treatment of post-transplant ureteral obstruction. PATIENTS AND METHODS: Data were reviewed for all patients who underwent percutaneous therapy for complications after renal transplantation between January 1985 and June 1995. A total of 61 patients with complications (leak, n = 17; obstruction, n = 44) had been treated. Patients underwent percutaneous nephrostomy followed by antegrade placement of a nephroureteral stent. In addition, all patients with obstruction also underwent ureteral balloon dilation. Follow-up ranged from 9 weeks to 24 months. Positive outcome was defined as nonsurgical closure of leak, significant improvement in renal function, and removal of the nephroureteral stent with maintenance of stable renal function. RESULTS: Regarding ureteral leak, 10 of 17 patients (59%) healed after treatment. Seven patients (41%) did not respond and went on to surgical repair. All patients with early (n = 13) ureteral obstruction (< 3 months after transplantation), had improved renal function (P < .025). Sixty-two percent of patients with early obstruction were cured (tube out with stable renal function) and 38% went to surgery for ureteral repair. In patients with late (n = 31) obstruction (> 3 months after transplantation), renal function improved in only 58% (P < .01). Only 16% of patients with late obstruction were cured (tube out with stable renal function). Ureteral obstruction was persistent in the remaining patients and did not respond to multiple balloon dilations. All complications were minor and included 23 of 61 (38%) patients with urinary tract infections and nine of 61 (14%) patients with limited hematuria. CONCLUSION: Percutaneous nephrostomy is very effective in improving renal function in patients with early obstruction. It is moderately successful in treating ureteral leak. Ureteral balloon dilatation is moderately effective for treatment of obstruction in the early (< 3 months) postoperative period. However, balloon dilation is minimally successful in curing ureteric obstruction occurring more than 3 months after transplantation. 相似文献
10.
A random sample of New London County, Connecticut, residents received a questionnaire about 9 mental health professions or professionals (MHPs): clergyperson, marriage and family counselor, nonpsychiatric physician, psychiatrist, psychiatric nurse, psychologist, psychotherapist, social worker, and telephone crisis counselor. Respondents defined each MHP and reported their satisfaction with treatment, which MHP they would recommend, their referral source(s), licensure requirements, and fees. A mixed-design ANOVA was computed, with comfortableness as the dependent variable; age, sex, saw an MHP, and education, the between-Ss variables; and the 9 MHPs, the within-Ss variable. A significant MHP effect showed that physicians were perceived as slightly more comfortable than were psychologists (nonsignificant), who, nevertheless, were perceived as exceeding all other trained MHPs in the comfortableness experienced by their clients. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献