全文获取类型
收费全文 | 1787篇 |
免费 | 18篇 |
专业分类
电工技术 | 15篇 |
综合类 | 2篇 |
化学工业 | 150篇 |
金属工艺 | 10篇 |
机械仪表 | 30篇 |
建筑科学 | 61篇 |
矿业工程 | 6篇 |
能源动力 | 58篇 |
轻工业 | 133篇 |
水利工程 | 11篇 |
石油天然气 | 6篇 |
无线电 | 231篇 |
一般工业技术 | 284篇 |
冶金工业 | 601篇 |
原子能技术 | 30篇 |
自动化技术 | 177篇 |
出版年
2021年 | 14篇 |
2020年 | 13篇 |
2019年 | 15篇 |
2018年 | 19篇 |
2017年 | 17篇 |
2016年 | 24篇 |
2015年 | 13篇 |
2014年 | 25篇 |
2013年 | 97篇 |
2012年 | 37篇 |
2011年 | 47篇 |
2010年 | 34篇 |
2009年 | 56篇 |
2008年 | 63篇 |
2007年 | 49篇 |
2006年 | 60篇 |
2005年 | 52篇 |
2004年 | 49篇 |
2003年 | 40篇 |
2002年 | 33篇 |
2001年 | 44篇 |
2000年 | 39篇 |
1999年 | 49篇 |
1998年 | 152篇 |
1997年 | 83篇 |
1996年 | 68篇 |
1995年 | 47篇 |
1994年 | 43篇 |
1993年 | 45篇 |
1992年 | 38篇 |
1991年 | 26篇 |
1990年 | 26篇 |
1989年 | 26篇 |
1988年 | 23篇 |
1987年 | 19篇 |
1986年 | 30篇 |
1985年 | 34篇 |
1984年 | 21篇 |
1983年 | 17篇 |
1982年 | 23篇 |
1981年 | 9篇 |
1980年 | 14篇 |
1979年 | 9篇 |
1978年 | 14篇 |
1977年 | 18篇 |
1976年 | 33篇 |
1974年 | 10篇 |
1973年 | 11篇 |
1972年 | 11篇 |
1968年 | 9篇 |
排序方式: 共有1805条查询结果,搜索用时 15 毫秒
91.
One hundred and five samples of pig backfat were assessed for appearance (colour and translucency) and hardness. The fatty acid profile of a selected subset of 50 samples was determined. Increased yellow colour was associated with increased linoleic and α-linolenic acid percentages. Increased translucency and fat softness were associated with decreased percentages of palmitic and stearic and oleic acid and a concurrent increase in the proportions of linoleic and α-linolenic acid. Oleic acid was found to be the single highest component (33.0-45.4%) and linoleic to show the greatest variation in range (9.8-28.4%). 相似文献
92.
The decline in pulsatile LH secretion and pituitary responsiveness to GnRH as pregnancy advances may be due to non-steroidal factors secreted by the ovine corpus luteum of pregnancy. Corpora lutea from ten ewes on days 70-80 of gestation were homogenized, charcoal-treated and, together with charcoal-treated follicular fluid from superovulated women, were subjected to inhibin immunoaffinity chromatography, reducing dimeric inhibin A and B by >90% and abolishing inhibin bioactivity. These preparations were investigated using cultures of rat pituitary cells. GnRH-induced LH and FSH secretion in vitro was reduced by ovine corpus luteum extract and human follicular fluid by 47+/-5% and 42+/-5% of control LH and by 37+/-5% and 50+/-10% of control FSH, respectively (P<0.001). Extracts prepared from corpora lutea and placentae that were collected on days 50, 90 and 120 of pregnancy (five ewes per stage of pregnancy) showed increased GnRH-induced LH-suppressing bioactivity, particularly in the case of the placental extracts, with a threefold increase in activity. When partially purified by pseudochromatofocusing, GnRH-induced LH-suppressing bioactivity in extracts of ovine corpora lutea was identified at pH 5.40 and 5.77. Although these values are similar to published gonadotrophin surge-attenuating factor (GnSAF) bioactivity pI values, a GnSAF-blocking antiserum had no consistent effect on ovine corpus luteum extract GnRH-induced LH-suppressing bioactivity. It was concluded that the ovine corpus luteum of pregnancy contains a non-steroidal, non-inhibin factor, probably not GnSAF, that has the ability to reduce pituitary responsiveness to GnRH in vitro. 相似文献
93.
The mathematical concept of the d-code and its associated contact graph give a model for sterically constrained addition patterns in fullerene derivatives C60Xm and C70Xm. In combination with simple electronic arguments, the stoichiometries, symmetries, and location of addends can be predicted, yielding a small number of candidates for further study. For example, sterically and optimal solutions C60Xm with pairwise separation of d bonds between addends are found at m(d) = 24(2), 12(3), 6(4,5), 2(6 to 9). The solution for C60X24 is unique, and the model selects 12 candidates for C60X12 from a starting set of 11661527060 possibilities. 相似文献
94.
Reconstituted orange juice inoculated with Salmonella Anatum, Salmonella Infantis, Salmonella Newport, or Salmonella Stanley was treated with gamma radiation at 2 degrees C. To determine the relationship between juice antioxidant power and Dgamma (dose required to achieve 90% mortality), juice solids were removed prior to inoculation by centrifugation and/or filtration to create juice preparations of varying turbidity. In unadulterated orange juice, Salmonella Anatum (Dgamma = 0.71 kGy) was significantly more resistant than the other species tested. Salmonella Newport (Dgamma = 0.48 kGy) and Salmonella Infantis (Dgamma = 0.35 kGy) were significantly different, while Salmonella Stanley (Dgamma = 0.38 kGy) was intermediate between the two. Neither the resistance of each isolate nor the pattern of relative resistance among isolates was altered in reduced turbidity juice preparations. Although total antioxidant power was associated with the level of juice solids resuspended in phosphate buffer, antioxidant power was not significantly associated with turbidity in the juice preparations or with Dgamma of any species. The variable resistance to irradiation of the Salmonella isolates suggests this as a more significant factor than turbidity or antioxidant power in designing antimicrobial juice irradiation protocols. 相似文献
95.
Michael J. Fowler Marylesa Howard Aaron Luttman Stephen E. Mitchell Timothy J. Webb 《Inverse Problems in Science & Engineering》2016,24(3):353-371
One of the primary causes of blur in a high-energy X-ray imaging system is the shape and extent of the radiation source, or ‘spot’. It is important to be able to quantify the size of the spot as it provides a lower bound on the recoverable resolution for a radiograph, and penumbral imaging methods – which involve the analysis of blur caused by a structured aperture – can be used to obtain the spot’s spatial profile. We present a Bayesian approach for estimating the spot shape that, unlike variational methods, is robust to the initial choice of parameters. The posterior is obtained from a normal likelihood, which was constructed from a weighted least squares approximation to a Poisson noise model, and prior assumptions that enforce both smoothness and non-negativity constraints. A Markov chain Monte Carlo algorithm is used to obtain samples from the target posterior, and the reconstruction and uncertainty estimates are the computed mean and variance of the samples, respectively. Synthetic data-sets are used to demonstrate accurate reconstruction, while real data taken with high-energy X-ray imaging systems are used to demonstrate applicability and feasibility. 相似文献
96.
D. S. Boyd 《International journal of remote sensing》2013,34(5):1017-1023
The use of middle infrared (MIR) radiation (3.0-5.0 mu m) at the regional scale may be unreliable for biophysical estimation, should be corrected for thermal emission and MIR reflectance used in its place. This study considered the potential use of MIR reflectance for studying tropical forests, with the relationship between MIR reflectance and estimated total biomass of the tropical forests of Cameroon derived. Comparisons were drawn with relationships between estimated total biomass and visible reflectance, near infrared reflectance, MIR radiation and surface temperature. Relationships between two vegetation indices, the NDVI and VI3, and estimated total biomass were also explored. It was found that correcting MIR radiation for thermal emission increased the strength of the relationship between radiation acquired in MIR wavelengths and estimated total biomass. The use of MIR reflectance, either alone or within the vegetation index VI3, provided the strongest relationship with estimated total biomass. This suggests that MIR reflectance may be more sensitive to changes in forest properties than the reflectance in visible and NIR wavelengths. It is recommended that MIR reflectance should be adopted more widely for the remote sensing of tropical forests. 相似文献
97.
Doreen S. Boyd Samuel Almond Jadunandan Dash Paul J. Curran Ross A. Hill 《International journal of remote sensing》2013,34(23):8421-8447
Given the close association between climate change and vegetation response, there is a pressing requirement to monitor the phenology of vegetation and understand further how its metrics vary over space and time. This article explores the use of the Envisat MERIS terrestrial chlorophyll index (MTCI) data set for monitoring vegetation phenology, via its estimates of chlorophyll content. The MTCI was used to construct the phenological profile of and extract key phenological event dates from woodland and grass/heath land in Southern England as these represented a range of chlorophyll contents and different phenological cycles. The period 2003–2008 was selected as this was known to be a period with temperature and phenological anomalies. Comparisons of the MTCI-derived phenology data were made with ground indicators and climatic proxy of phenology and with other vegetation indices: MERIS global vegetation index (MGVI), MODIS normalized difference vegetation index (NDVI) and MODIS enhanced vegetation index (EVI). Close correspondence between MTCI and canopy phenology as indicated by ground observations and climatic proxy was evident. Also observed was a difference between MTCI-derived phenological profile curves and key event dates (e.g. green-up, season length) and those derived from MERIS MGVI, MODIS NDVI and MODIS EVI. The research presented in this article supports the use of the Envisat MTCI for monitoring vegetation phenology, principally due to its sensitivity to canopy chlorophyll content, a vegetation property that is a useful proxy for the canopy physical and chemical alterations associated with phenological change. 相似文献
98.
D. S. Boyd P. C. Phipps G. M. Foody R. P. D. Walsh 《International journal of remote sensing》2013,34(23):5141-5147
The ever-wet tropics are under threat from ENSO events and there is a need for a monitoring system to analyse and describe their responses to such events. This letter explores the relative value of using NOAA AVHRR middle infrared (MIR) reflectance data and NDVI data for the monitoring of ENSO-related drought stress of a tropical forest ecosystem in Sabah, Malaysia. Relationships between rainfall and MIR reflectance were examined. Correlation coefficients are generally large and significant (at 0.1 level) while those between rainfall and NDVI were small and insignificant. This letter concludes that there is potential in using MIR reflectance for monitoring the effects of ENSO-induced drought stress on these forests and this has a bearing on how NOAA AVHRR data may be used to further our knowledge on the impacts of ENSO events on tropical forest environments. 相似文献
99.
Glen R. Boyd Prasad Shetty Anne M. Sandvig Gregory L. Pierson 《Canadian Metallurgical Quarterly》2004,130(10):1188-1197
The concentrations of total, colloidal, and truly dissolved lead (Pb) were investigated in tap water following laboratory simulations of partial lead pipe replacements. Old lead pipes were recovered from service in New Orleans, La and mounted horizontally in an experimental apparatus at Tulane Univ. Municipal water was diverted for two weeks at low flowrates of 0.2 or 1.1?L/min (0.05 or 0.3?gal/min) through two pipe trains operated continuously and two pipe trains operated intermittently. Samples were collected to determine relative concentrations and time needed for each form of Pb (total, colloidal, and truly dissolved) to stabilize below the U.S. Environmental Protection Agency action level (AL) of 15?μg/L Pb. Results demonstrate that total Pb concentrations exceeded the AL immediately following simulated partial pipe replacements. In most cases, total Pb concentrations were reduced below the AL by flushing for 15–30?min but subsequent sampling revealed total Pb concentrations greater than the AL. Continuous flow pattern flushing was more effective at stabilizing total Pb concentrations below the AL than intermittent flows. Results also demonstrate that colloidal Pb concentrations were 38–54% of total Pb and truly dissolved Pb concentrations were 41–60% of total Pb concentrations after stabilization. 相似文献
100.
S Kozlowski M Corr M Shirai LF Boyd CD Pendleton JA Berzofsky DH Margulies 《Canadian Metallurgical Quarterly》1993,151(8):4033-4044
T cell stimulation by certain class I-restricted antigenic peptides, such as the HIV 1 gp160-derived peptide, P18, requires peptide processing by angiotensin-1 converting enzyme (ACE) in FCS. We observed that longer versions of P18 and the murine cytomegalovirus pp89-derived core peptide, pMCMV, which could stimulate T cell hybridomas in FCS, were not as sensitive to the ACE inhibitor captopril as P18. Using cell-free soluble murine class I MHC molecules and protease inhibitors, we found that there are pathways of differing efficiency that use enzymes other than ACE for the proteolytic processing of peptides in serum. The kinetics of the generation of T cell stimulatory activity among P18 variant peptides in serum differed with peptide length, and with the nature of amino and COOH-terminal extensions. Such processing occurs in human plasma as well as in FCS. The understanding of this processing, its kinetics, and its inhibitors can lead to better design of peptide-based therapies, including vaccines. 相似文献