全文获取类型
收费全文 | 9165篇 |
免费 | 1003篇 |
国内免费 | 57篇 |
专业分类
电工技术 | 8篇 |
综合类 | 144篇 |
化学工业 | 3963篇 |
金属工艺 | 56篇 |
机械仪表 | 86篇 |
建筑科学 | 174篇 |
矿业工程 | 22篇 |
能源动力 | 157篇 |
轻工业 | 5091篇 |
水利工程 | 32篇 |
石油天然气 | 139篇 |
武器工业 | 1篇 |
无线电 | 42篇 |
一般工业技术 | 223篇 |
冶金工业 | 27篇 |
原子能技术 | 21篇 |
自动化技术 | 39篇 |
出版年
2024年 | 34篇 |
2023年 | 155篇 |
2022年 | 209篇 |
2021年 | 383篇 |
2020年 | 318篇 |
2019年 | 313篇 |
2018年 | 302篇 |
2017年 | 357篇 |
2016年 | 413篇 |
2015年 | 377篇 |
2014年 | 471篇 |
2013年 | 707篇 |
2012年 | 600篇 |
2011年 | 667篇 |
2010年 | 452篇 |
2009年 | 477篇 |
2008年 | 456篇 |
2007年 | 502篇 |
2006年 | 409篇 |
2005年 | 295篇 |
2004年 | 244篇 |
2003年 | 228篇 |
2002年 | 202篇 |
2001年 | 143篇 |
2000年 | 218篇 |
1999年 | 141篇 |
1998年 | 165篇 |
1997年 | 103篇 |
1996年 | 135篇 |
1995年 | 111篇 |
1994年 | 94篇 |
1993年 | 96篇 |
1992年 | 101篇 |
1991年 | 86篇 |
1990年 | 53篇 |
1989年 | 34篇 |
1988年 | 19篇 |
1987年 | 28篇 |
1986年 | 31篇 |
1985年 | 19篇 |
1984年 | 19篇 |
1983年 | 10篇 |
1982年 | 8篇 |
1981年 | 6篇 |
1980年 | 12篇 |
1979年 | 3篇 |
1978年 | 6篇 |
1976年 | 5篇 |
1975年 | 3篇 |
1974年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
102.
P.?N.?Mayamol T.?Samuel C.?Balachandran A.?Sundaresan C.?ArumughanEmail author 《Journal of the American Oil Chemists' Society》2004,81(4):407-413
Several pilot-scale trials reported in this paper, using palm stearin-rice bran oil (PS-RBO) blends, obviously did not contain
trans FA (TFA), whereas the commercial products were found to contain 18–27% TFA. The effects of processing conditions such as
rate of agitation, crystallization temperature, and composition of the blends on the crystal structure of shortenings were
studied. The products were evaluated for their physicochemical characteristics using DSC, X-ray diffraction (XRD), HPLC, and
FTIR techniques. The formulation containing 50% PS and 50% RBO showed melting and cooling characteristics similar to those
of hydrogenated commercial “vanaspati” samples. Analysis of the FA composition revealed that the formulated shortenings contained
15–19% C18∶2 PUFA. Tocopherol and tocotrienol contents of the experimental shortenings were in the range of 850–1000 ppm with oryzanol
content up to 0.6%. XRD studies demonstrated that the crystal form in the shortenings was predominantly the most stable β′
form, and there was less of the undesirable β form. 相似文献
103.
Joseph C. Goffreda Martha A. Mutschler Dirk A. Avé Ward M. Tingey John C. Steffens 《Journal of chemical ecology》1989,15(7):2135-2147
Settling of the potato aphid,Macrosiphum euphorbiae, on feeding membranes was deterred by methanolic leaf rinses ofLycopersicon pennellii, or of its F1 with tomato,L. esculentum. The active compounds in theL. pennellii rinsates were identified as 2,3,4-tri-O-acylglucoses bearing short to medium chain length fatty acids. These compounds are localized in the glandular exudate of the type IV trichomes and may accumulate to levels in excess of 400 g/cm2. In choice assays, purified glucose esters fromL. pennellii reduced aphid settling at concentrations as low as 25 g/cm2; at concentrations of 150 g/cm2 or more, all aphids avoided treated areas. Glucose esters were also active in deterring aphid settling in no-choice assays. At 100 g/ cm2, these esters resulted in increased levels of mortality after 48 hr. 相似文献
104.
A Flavanone and Two Phenolic Acids from Chrysanthemum morifolium with Phytotoxic and Insect Growth Regulating Activity 总被引:2,自引:0,他引:2
Beninger CW Abou-Zaid MM Kistner AL Hallett RH Iqbal MJ Grodzinski B Hall JC 《Journal of chemical ecology》2004,30(3):589-606
Leaves of Chrysanthemum morifolium cv. Ramat were extracted sequentially with hexane, ethyl acetate, and methanol. The methanol fraction, when incorporated into artificial diet was found to reduce the growth of cabbage looper (Trichoplusia ni Hubner) larvae at concentrations between 500 and 5000 ppm of diet. Fractionation of the methanol extract on a Sephadex column yielded five fractions, three of which reduced the weight of larvae relative to the control. One fraction was analyzed using high performance liquid chromatography (HPLC) and found to contain three main constituents. These compounds were purified using a combination of gel permeation chromatography on Sephadex LH20 and HPLC, and analyzed by 1H and 13CNMR as well as undergoing chemical and physical analyses. The compounds were identified as: 1, chlorogenic acid (5-O-caffeoylquinic acid); 2, 3,5-O-dicaffeoylquinic acid; and 3, 3', 4',5-trihydroxyflavanone7-O-glucuronide (eriodictyol7-O-glucuronide). At concentrations between 100 to 1000 ppm these compounds reduced both growth and photosynthesis of Lemna gibba L. with the order of efficacy being: flavanone > chlorogenic acid > 3,5-O-dicaffeoylquinic acid. Furthermore, when incorporated separately into artificial diet these compounds, at 10 to 1000 ppm, enhanced or reduced growth of the cabbage looper (Trichoplusia ni) and gypsy moth (Lymantria dispar L.). 相似文献
105.
Maritza F. Díaz Gómez Goitybell Martínez Téllez Maikel Arteaga Cruz Rafael Garcés Mancheno 《Journal of the American Oil Chemists' Society》2006,83(11):943-946
Ozonized theobroma fat is used as raw material in the manufacture of pessaries and cosmetic creams. Ozonization of theobroma
fat with water was carried out at different applied ozone dosages, and the resultant PV, acid value, iodine value, total hydroperoxide
content, and FA content were determined. PV and total hydroperoxide content showed a notable increase with applied ozone dosage
up to 35.7 mg/g. Acid value varied slightly from 4.1 to 9.9 mg KOH/g, and the iodine value fell to zero. PV and total hydroperoxide
content increased slightly with a higher applied ozone dosage. The comparison of total hydroperoxide measurement using ferrous
oxidation in xylenol orange assay and traditional iodometric assay for PV determination showed a significant linear correlation.
Small amounts of oleic acid were found in ozonized theobroma fat samples with iodine value equaling zero, which demonstrated
that iodine value determination is an inexact assay. During ozonization of theobroma fat, an increase in acid value of 18.9-fold
with respect to the initial value was observed owing to decomposition of peroxide. 相似文献
106.
107.
An improved allelopathic correlation between phytotoxicity measured in root growth bioassay upon annual ryegrass (Lolium rigidum Gaud.) and the concentrations of a selection of dynamically produced allelochemicals quantified in the root exudates of cv. Khapli wheat (Triticum turgidum ssp. durum (Desf.) Husn.) monitored during the first 15 days of wheat seedling growth in a sterile, agar–water medium, has been established. Changes over the 15-day growth period in the quantities of five exuded benzoxazinones and seven phenolic acids were measured simultaneously using GC/MS/MS. Substantiating pure compound dose–response measurements were conducted over a range of concentrations for the putative allelochemicals within the wheat exudates. One synergism-based proposal using the monitored compounds to explain the observed low-exudate-concentration phytotoxicity was explored, but was found to be experimentally inadequate. 相似文献
108.
Why Phenolic Acids Are Unlikely Primary Allelochemicals in Rice 总被引:21,自引:0,他引:21
Olofsdotter M Rebulanan M Madrid A Dali W Navarez D Olk DC 《Journal of chemical ecology》2002,28(1):229-242
Allelopathy in rice (Oryza sativa, L.) effective against weeds has been found in about 3.5% of tested rice germplasm in both laboratory and field experimentation. However, the allelochemicals responsible for growth inhibition of rice-associated weeds have not yet been identified. In the literature, phenolic acids are often mentioned as putative allelochemicals. If phenolic acids commonly reach growth inhibitory concentrations in rice ecosystems, it must be expected that the degree of tolerance to phenolic acids will vary among traditional rice cultivars or plant species adapted to rice environments having inherently different phenolic acid concentrations. Phenolic acids concentrations are normally greater in submerged than in aerobic soils. A dose–response study, however, showed that seedlings of rice cultivars adapted to submerged anaerobic soils did not have higher level of tolerance against p-hydroxybenzoic acid than did seedlings of varieties adapted to aerobic upland soils. Moreover, traditional rice cultivars had no greater tolerance than did improved cultivars that were recently bred for traits other than tolerance of phenolic acids. Similarly, there were no differences in tolerance of p-hydroxybenzoic acid between two Echinochloa weed species adapted to either anaerobic or aerobic growth conditions. Thus, neither the rice cultivars nor weed species had evolved different tolerance levels against the phenolic acid. However, all rice cultivars had significantly greater tolerance of p-hydroxybenzoic acid than did either weed species. In a second experiment, the rates at which rice plants released phenolic acids into solution cultures were measured for at least one month, the time period of greatest allelopathic activity following planting under field conditions. The maximum release rate of phenolic acids during the first month of growth was approximately 10 g/plant/day. At a conventional plant density, the release rate of phenolic acids would be approximately 1 mg/m2day. This order of release rate cannot provide concentrations remotely close to phytotoxic levels determined for these rice cultivars and weed species. The results presented in this paper do not preclude the possibility that phenolic acids might be one component in a mixture of chemicals that, when present simultaneously, are allelopathic. 相似文献
109.
A. Proctor C. Adhikari G. D. Blyholder 《Journal of the American Oil Chemists' Society》1996,73(6):693-698
The structures of and lipid complexes with two commercial silica hydrogels (Trisyl and Sorbsil 40), which contain about 60%
moisture, were examined by diffuse reflectance Fourier transform infrared spectroscopy. The spectra suggested that Trisyl
contained less moisture than Sorbsil 40. However, the silanol groups of Sorbsil 40 were more active in adsorbing oleic acid,
triglyceride, and phosphatidylcholine (PC) from hexane than those of Trisyl. Both adsorbents strongly bound PC through the
PC carbonyl and phosphate groups. Lipid adsorption from hexane solution by Trisyl depended solely on trapped moisture, while
Sorbsil 40 used moisture and silanol groups on the silica surface. Spectra of triglyceride-silica hydrogel complexes, obtained
24 and 72 h after obtaining the initial spectra, showed that Sorbsil 40 adsorption was by Van der Waals forces, but the triglyceride
reoriented over time with an increase in hydrogen bonding. In contrast, Trisyl initially adosorbed triglyceride by hydrogen
bonding which was stable for at least 72 h. 相似文献
110.
Hai -Hang Li Masafumi Inoue Hiroyuki Nishimura Junya Mizutani Eiji Tsuzuki 《Journal of chemical ecology》1993,19(8):1775-1787
Phenolic compounds have been identified as the most common allelochemicals produced by higher plants. Inhibitions of cinnamic acid, its related phenolic derivatives, and abscisic acid (ABA) on seedling growth and seed germination of lettuce were studied.trans-Cinnamic acid, ando-,m-, andp-coumaric acids inhibited the growth of etiolated seedlings of lettuce at concentrations higher than 10–4 M and seed germination above 10–3 M. Coumarin inhibited seedling growth and seed germination at 10–5 M or above. Chlorogenic acid inhibited seedling growth above 10–4 M, but did not inhibit seed germination at 10–5–5×10–3 M. Low concentrations (below 10–3 M) of caffeic and ferulic acids promoted the elongation of hypocotyls, but higher concentrations (over 10–3 M) inhibited seedling growth and seed germination. These phenolic compounds and abscisic acid had additive inhibitory effects both on seedling growth and seed germination. The inhibition on lettuce was reversed by caffeic and ferulic acids at concentrations lower than 10–3 M except for the inhibition of germination by coumarin. These results suggest that in naturetrans-cinnamic acid,o-, m-, p-coumaric acids, coumarin, and chlorogenic acid inhibit plant growth regardless of their concentration. However, caffeic and ferulic acids can either promote or inhibit plant growth according to their concentration. 相似文献