全文获取类型
收费全文 | 3669篇 |
免费 | 68篇 |
国内免费 | 4篇 |
专业分类
电工技术 | 40篇 |
综合类 | 4篇 |
化学工业 | 426篇 |
金属工艺 | 232篇 |
机械仪表 | 72篇 |
建筑科学 | 131篇 |
矿业工程 | 88篇 |
能源动力 | 89篇 |
轻工业 | 263篇 |
水利工程 | 38篇 |
石油天然气 | 4篇 |
无线电 | 329篇 |
一般工业技术 | 535篇 |
冶金工业 | 1057篇 |
原子能技术 | 37篇 |
自动化技术 | 396篇 |
出版年
2022年 | 29篇 |
2021年 | 57篇 |
2020年 | 33篇 |
2019年 | 41篇 |
2018年 | 37篇 |
2017年 | 35篇 |
2016年 | 50篇 |
2015年 | 40篇 |
2014年 | 60篇 |
2013年 | 184篇 |
2012年 | 116篇 |
2011年 | 166篇 |
2010年 | 116篇 |
2009年 | 127篇 |
2008年 | 124篇 |
2007年 | 141篇 |
2006年 | 122篇 |
2005年 | 95篇 |
2004年 | 80篇 |
2003年 | 79篇 |
2002年 | 71篇 |
2001年 | 64篇 |
2000年 | 76篇 |
1999年 | 63篇 |
1998年 | 283篇 |
1997年 | 173篇 |
1996年 | 143篇 |
1995年 | 85篇 |
1994年 | 78篇 |
1993年 | 106篇 |
1992年 | 47篇 |
1991年 | 42篇 |
1990年 | 35篇 |
1989年 | 42篇 |
1988年 | 25篇 |
1987年 | 34篇 |
1986年 | 38篇 |
1985年 | 34篇 |
1984年 | 32篇 |
1983年 | 28篇 |
1982年 | 29篇 |
1981年 | 34篇 |
1980年 | 33篇 |
1979年 | 26篇 |
1978年 | 27篇 |
1977年 | 59篇 |
1976年 | 72篇 |
1974年 | 32篇 |
1973年 | 32篇 |
1972年 | 24篇 |
排序方式: 共有3741条查询结果,搜索用时 15 毫秒
71.
72.
A scheme for attachment of psychiatric nurses from hospital to group practice in Oxford is described. One community psychiatric nurse can work satisfactorily with eight general practitioners covering a population of about 18,000. From analysis of a working year, it is concluded that this arrangement improves the care of patients in the community by providing psychiatric help at times when it was previously unavailable or unacceptable.The implications of such a scheme for the workings of the primary health care team and the hospital psychiatric service are considered, and a case is made for a further study involving a comparison between practices with and without the attachment of a community psychiatric nurse. 相似文献
73.
An automatic quadrature algorithm especially designed for double integration of functions with some form of singular behaviour on the boundary of the integration region is described, and its FORTRAN code is presented. The algorithm is based on the use of the product trapezoidal rule, after a non-linear transformation of the integrand in both variables renders a new integrand function whose derivatives vanish on the (transformed) boundary. Numerical results demonstrate the ability of the algorithm to obtain high accuracies in dealing automatically with pathological singularities of non-specific types. 相似文献
74.
Jijin R. A. Kuttiyatveetil Pranabendu Mitra Darren Goldin Michael T. Nickerson Takuji Tanaka 《International Journal of Food Science & Technology》2019,54(4):1130-1140
The present research develops an innovative nutrient recovery strategy for capturing of un-utilised nutrients from agri-food byproducts using a combination of solid state fermentation (SSF) and insect rearing. SSF of borage and flaxseed meals were performed using GRAS organisms to release indigenous nutrients and to produce additional nutrients. Proximate analysis of the SSF-meals showed increases in both lipid and protein contents. Black soldier fly larvae (BSFL) were then grown on these SSF-meals for 12 day. The meals fermented singularly with Lactobacillus plantarum or Aspergillus niger displayed up to 30% enhancement in BSFL biomass, and dual fermentation with L. plantarum and Aspergillus oryzae resulted in an additional 10% enhancement. These examinations showed SFL use over-90% of proteins and lipids in SSF-meals. The results indicate that fermentation of these low-value meals can boost the efficacy of larval growth and the recovery of nutrients from agricultural byproducts as larval biomass. 相似文献
75.
Effects of dilution on fine particle mass and partitioning of semivolatile organics in diesel exhaust and wood smoke 总被引:1,自引:0,他引:1
Experiments were conducted to examine the effects of dilution on fine particle mass emissions from a diesel engine and wood stove. Filter measurements were made simultaneously using three dilution sampling systems operating at dilution ratios ranging from 20:1 to 510:1. Denuders and backup filters were used to quantify organic sampling artifacts. For the diesel engine operating at low load and wood combustion, large decreases in fine particle mass emissions were observed with increases in dilution. For example, the PM2.5 mass emission rate from a diesel engine operating at low load decreased by 50% when the dilution ratio was increased from 20:1 to 350:1. Measurements of organic and elemental carbon indicate that the changes in fine particle mass with dilution are caused by changes in partitioning of semivolatile organic compounds. At low levels of dilution semivolatile species largely occur in the particle phase, but increasing dilution reduces the concentration of semivolatile species, shifting this material to the gas phase in order to maintain phase equilibrium. Emissions of elemental carbon do not vary with dilution. Organic sampling artifacts are shown to vary with dilution because of the combination of changes in partitioning coupled with adsorption of gas-phase organics by quartz filters. The fine particle mass emissions from the diesel engine operating at medium load did not vary with dilution because of the lower emissions of semivolatile material and higher emissions of elemental carbon. To measure partitioning of semivolatile materials under atmospheric conditions, partitioning theory indicates that dilution samplers need to be operated such that the diluted exhaust achieves atmospheric levels of dilution. Too little dilution can potentially overestimate the fine particle mass emissions, and too much dilution (with clean air) can underestimate them. 相似文献
76.
77.
The effects of concentrate to forage ratio and sodium bicarbonate (buffer) supplementation on intake, ruminal fermentation characteristics, digestibility coefficients, milk yield, and milk composition were examined in 4 cannulated Holstein cows (100 +/- 20 d in milk). A 4 x 4 Latin square design with 2 x 2 factorial arrangement of treatments was implemented for 3-wk experimental periods. The 4 treatments were a 50:50 concentrate to forage ratio with 1.2% of dry matter (DM) and without added buffer and a 75:25 concentrate to forage ratio with (1.2% of DM) and without (0% of DM) buffer. The forage component of the ration was a 50:50 mixture of alfalfa and barley and triticale silage, and diets were fed ad libitum as a total mixed ration. Although feed intake was not influenced by treatments, substantial treatment differences were observed for milk yield and milk composition. Cows fed high-concentrate diet had lower ruminal pH, ruminal acetate, and butyrate concentrations, whereas propionate concentrations were significantly elevated. The addition of buffer, at both levels of concentrate inclusion, resulted in elevated total volatile fatty acids and acetate concentrations. We concluded that altering the forage concentrate ratio in the diet of lactation cows influenced milk yield and milk composition, but the addition of buffer to the diet prevented the elevation in trans-C18:1 fatty acids in milk fat, and related milk fat depression, associated with feeding high-concentrate diets. 相似文献
78.
Philip O Owuor John E Orchard Janet M Robinson Sarah J Taylor 《Journal of the science of food and agriculture》1990,52(1):55-61
The chemical composition of black teas (Camellia sinensis L) varies when the green leaf from which they are manufactured is withered physically to the same degree but for different periods. Caffeine contents progressively increase with prolonged withering time whereas theaflavins decrease due to prolonged withering. Although the sums of group I and group II volatile flavour compounds (VFC) decrease with prolonged withering time, the flavour index (expressed as group II VFC/group I VFC) increases due to prolonged withering. No significant changes were noted in the thearubigin levels with variation in withering time, but the tasters' evaluations were at a maximum for teas withered for 14 h. Subsequently the evaluation decreased with longer withering times. 相似文献
79.
Volk C Kaplan LA Robinson J Johnson B Wood L Zhu HW LeChevallier M 《Environmental science & technology》2005,39(11):4258-4264
Natural organic matter (NOM) in drinking water supplies can provide precursors for disinfectant byproducts, molecules that impact taste and odors, compounds that influence the efficacy of treatment, and other compounds that are a source of energy and carbon for the regrowth of microorganisms during distribution. NOM, measured as dissolved organic carbon (DOC), was monitored daily in the White River and the Indiana-American water treatment plant over 22 months. Other parameters were either measured daily (UV-absorbance, alkalinity, color, temperature) or continuously (turbidity, pH, and discharge) and used with stepwise linear regressions to predict DOC concentrations. The predictive models were validated with monthly samples of the river water and treatment plant effluent taken over a 2-year period after the daily monitoring had ended. Biodegradable DOC (BDOC) concentrations were measured in the river water and plant effluent twice monthly for 18 months. The BDOC measurements, along with measurements of humic and carbohydrate constituents within the DOC and BDOC pools, revealed that carbohydrates were the organic fraction with the highest percent removal during treatment, followed by BDOC, humic substances, and refractory DOC. 相似文献
80.
Sorrell DA Szymanowska M Boutinaud M Robinson C Clarkson RW Stein T Flint DJ Kolb AF 《The Journal of dairy research》2005,72(4):433-441
The mammary gland undergoes extensive tissue remodelling during each lactation cycle. During pregnancy, the epithelial compartment of the gland is vastly expanded (Benaud et al. 1998). At the end of lactation the epithelial cells undergo apoptosis and adipocyte differentiation is induced (Lilla et al. 2002). Ductal and alveolar growth during puberty and pregnancy, and the involution process require the action of proteolytic enzymes (including matrix metalloproteinases, plasminogen and membrane-peptidases) and the corresponding genes are activated during these periods (Benaud et al. 1998; Alexander et al. 2001). Matrix metalloproteinases (MMP) are expressed in several cell types of the mammary gland including stromal fibroblasts (e.g., MMP3, MMP2), epithelial cells (e.g., MMP7 or MMP9), adipocytes (e.g., MMP2) and lymphoid cells (e.g., MMP9) (Crawford et al. 1996; Lund et al. 1996; Wiseman et al. 2003). A number of knock-out mice, which are deficient for individual MMP genes (e.g., MMP2, MMP3) or plasminogen, display alterations to mammary gland structure and impairment of lactation (Lund et al. 1999; Wiseman et al. 2003). 相似文献