全文获取类型
收费全文 | 9156篇 |
免费 | 336篇 |
国内免费 | 233篇 |
出版年
2023年 | 96篇 |
2022年 | 148篇 |
2021年 | 138篇 |
2020年 | 194篇 |
2019年 | 215篇 |
2018年 | 223篇 |
2017年 | 189篇 |
2016年 | 183篇 |
2015年 | 187篇 |
2014年 | 316篇 |
2013年 | 517篇 |
2012年 | 202篇 |
2011年 | 345篇 |
2010年 | 234篇 |
2009年 | 347篇 |
2008年 | 361篇 |
2007年 | 419篇 |
2006年 | 347篇 |
2005年 | 310篇 |
2004年 | 281篇 |
2003年 | 294篇 |
2002年 | 262篇 |
2001年 | 246篇 |
2000年 | 232篇 |
1999年 | 223篇 |
1998年 | 217篇 |
1997年 | 223篇 |
1996年 | 216篇 |
1995年 | 238篇 |
1994年 | 225篇 |
1993年 | 191篇 |
1992年 | 182篇 |
1991年 | 135篇 |
1990年 | 127篇 |
1989年 | 125篇 |
1988年 | 79篇 |
1987年 | 90篇 |
1986年 | 66篇 |
1985年 | 138篇 |
1984年 | 149篇 |
1983年 | 90篇 |
1982年 | 102篇 |
1981年 | 101篇 |
1980年 | 106篇 |
1979年 | 66篇 |
1978年 | 57篇 |
1977年 | 59篇 |
1976年 | 59篇 |
1975年 | 51篇 |
1974年 | 43篇 |
排序方式: 共有9725条查询结果,搜索用时 20 毫秒
991.
Zhanar A. Kozhamkulova Mohamed M. Radwan Galiya E. Zhusupova Zharilkasin A. Abilov Samir A. Ross 《Phytochemistry letters》2011,4(3):323-327
Halimodendrin I, a new acylated triterpene glycoside (1), was isolated and chemically characterized as 3β-O-palmitoyl-28-[3′-palmitoyl-β-d-glucopyranosyl]-olean-12-en-28-oic acid from the aerial part of Halimodendron halodendron (Fabaceae) by IR, 1D and 2D NMR, HR-ESI-MS and LR-ESI-MS experiments. In addition, seven known compounds were isolated and identified as: palmitic acid, glycerol-2-linoleneate, glycerol-1,3-dilinoleneate, ferulic acid, 3-O-methylquercetin, β-sitosterol, and β-sitosterol-3-O-β-d-glucopyranoside. Nine fatty acids were identified and quantified in the saponifiable matter of the hexane extract. These fatty acids are: myristic, n-pentadecanoic, palmitoleic, palmitic, linoleic, oleic, stearic, arachidic, and behenic acids. The volatile oil was isolated by hydrodistillation (0.013%, w/w) with unpleasant smell. Twenty-seven components were identified in the oil by GC/MS. 相似文献
992.
Gjerlaug-Enger E Kongsro J Aass L Odegård J Vangen O 《Animal : an international journal of animal bioscience》2011,5(11):1829-1841
This study was conducted to evaluate the potential of near-infrared (NIR) spectroscopy (NIRS) technology for prediction of the chemical composition (moisture content and fatty acid composition) of fat from fast-growing, lean slaughter pig samples coming from breeding programmes. NIRS method I: a total of 77 samples of intact subcutaneous fat from pigs were analysed with the FOSS FoodScan NIR spectrophotometer (850 to 1050 nm) and then used to predict the moisture content by using partial least squares (PLS) regression methods. The best equation obtained has a coefficient of determination for cross-validation (CV; R(2)(cv)) and a root mean square error of a CV (RMSECV) of 0.88 and 1.18%, respectively. The equation was further validated with (n = 15) providing values of 0.83 and 0.42% for the coefficient of determination for validation (R(2)(val)) and root mean square error of prediction (RMSEP), respectively. NIRS method II: in this case, samples of melted subcutaneous fat were analysed in an FOSS XDS NIR rapid content analyser (400 to 2500 nm). Equations based on modified PLS regression methods showed that NIRS technology could predict the fatty acid groups, the main fatty acids and the iodine value accurately with R(2)(cv), RMSECV, R(2)(val) and RMSEP of 0.98, 0.38%, 0.95 and 0.49%, respectively (saturated fatty acids), 0.94, 0.45%, 0.97 and 0.65%, respectively (monounsaturated fatty acids), 0.97, 0.28%, 0.99 and 0.34%, respectively (polyunsaturated fatty acids), 0.76, 0.61%, 0.84 and 0.87%, respectively (palmitic acid, C16:0), 0.75, 0.16%, 0.89 and 0.10%, respectively (palmitoleic acid, C16:1n-7), 0.93, 0.41%, 0.96 and 0.64%, respectively (steric acid, C18:0), 0.90, 0.51%, 0.94 and 0.44%, respectively (oleic acid, C18:1n-9), 0.97, 0.25%, 0.98 and 0.29% (linoleic acid, C18:2n-6), 0.68, 0.09%, 0.57 and 0.16% (α-linolenic acid, C18:3n-3) and 0.97, 0.57, 0.97 and 1.22, respectively (iodine value, calculated). The magnitude of this error showed quite good accuracy using these rapid methods in prediction of the moisture and fatty acid composition of fat from pigs involved in breeding schemes. 相似文献
993.
The first limiting nutrients in typical laying hen diets are the sulphur-containing amino acids and, in particular, methionine. To fulfil the birds' recommended requirement, conventional diets are supplemented with synthetic methionine. As this is not allowed in organic production it becomes very important to have access to alternative high-quality protein feed ingredients. An experiment was performed to evaluate the possibility to compose a diet with 100% organically approved feed ingredients using mussel meal as a major source of methionine. The experiment included 678 Lohman Selected Leghorn (LSL) and 678 Hyline White, W-98, layers during 20 to 72 weeks of age. There were 12 aviary pens with 113 birds in each. The birds were fed one of the two experimental diets containing either 3.5% or 7% dried mussel meat meal or a commercial organic diet from a Swedish feed manufacturer for comparison. Production and mortality were recorded daily per group, and egg weight was recorded once weekly. At 33, 55 and 70 weeks, 10 eggs from each treatment group were collected and analysed for internal egg quality. Diets had no significant effect on laying percentage, egg mass, feed intake, feed conversion ratio, mortality, bird live weight or proportion misplaced, cracked or dirty eggs. Egg quality, that is, shell deformation, shell breaking strength, albumen height, shell percentage and proportion of blood and meat spots were also unaffected. There was a significant difference in egg yolk pigmentation, that is, the egg yolk was more coloured when feeding 7% mussel meal compared with the other diets. Hyline hens had lower feed intake and laying percentage, and higher egg weight, but lower egg mass production than LSL birds. The age of the birds influenced all egg quality traits except for meat and blood spots. The dry matter of the excreta was significantly lower for both genotypes fed the 7% mussel meal diet. These results indicate that mussels may be a high-quality protein source and may replace fishmeal in organic diets for layers. 相似文献
994.
995.
996.
997.
998.
The leaf protein content for 17 species of legumes ranges from 2.8 to 9.4 g% fr. wt, with an average of 5.3 g % fr. wt. Taxonomic pattern is detectable in leaf amino acid patterns, those of the Mimosoideae being distinguishable from those of the Papilionoideae and Caesalpinioideae. 相似文献
999.
Ferdinand Bohlmann Christa Zdero Robert M. King Harold Robinson 《Phytochemistry》1984,23(5):1185-1187
Perymenium featherstonei afforded, in addition to the known ent-kaurene derivative 4α, 15-dihydroencelin, two closely related epimeric acids. 相似文献
1000.
The utilization and translocation of nitrogen was investigated in exponentially growing, nitrogen-limited Pisum sativum L. cv. Marma. The plants were given N daily at exponentially increasing, although suboptimal, relative nitrogen addition rates (RN) calculated to yield a relative increment in N of 0.06 day?1 and 0.12 day?1. After 10 days of NO?3 additions (26 days after sowing), the relative growth rate more or less equaled RN. Uptake of NO?3 was several-fold higher than the N requirement for the growth rate set by RN. The daily addition of NO?3 was taken up after 7 to 8 h, resulting in a cyclic behaviour in the NO?3 utilization. During the phase of net NO?3 influx, the filling phase (0 to 8 h), in vitro nitrate reductase activity (NR activity) and intracellular levels of soluble N in the root increased. In the phase of no net influx of NO?3 the depletion phase (8 to 24 h), the plants were entirely dependent on stored N. During this phase both in vitro NR activity and intracellular levels of soluble N decreased. Also the calculated actual rate of NO?3 reduction was high in the filling phase, while it was close to zero in the depletion phase. The pattern of these fluctuations indicates that the regulation of NO?3 utilization involves an interplay between transmembrane fluxes of NO?3, the cytosolic NO?3 concentration and NR activity. Cyclic fluctuations in N-containing compounds were also found in the xylem. Nitrogen was mainly transported as amino acids. The pattern of NO?3 transport in the xylem and the fluctuations in the shoot of in vitro NR activity indicate that a reasoning similar to that for the regulation of NO?3 assimilation in the root also applies for the shoot. The results also indicate a substantial supply of amino acids to the xylem through recirculation from the shoot. 相似文献