全文获取类型
收费全文 | 3456篇 |
免费 | 235篇 |
国内免费 | 240篇 |
出版年
2023年 | 69篇 |
2022年 | 59篇 |
2021年 | 99篇 |
2020年 | 113篇 |
2019年 | 137篇 |
2018年 | 98篇 |
2017年 | 158篇 |
2016年 | 146篇 |
2015年 | 110篇 |
2014年 | 146篇 |
2013年 | 293篇 |
2012年 | 121篇 |
2011年 | 206篇 |
2010年 | 120篇 |
2009年 | 181篇 |
2008年 | 183篇 |
2007年 | 212篇 |
2006年 | 167篇 |
2005年 | 157篇 |
2004年 | 95篇 |
2003年 | 100篇 |
2002年 | 106篇 |
2001年 | 81篇 |
2000年 | 72篇 |
1999年 | 64篇 |
1998年 | 54篇 |
1997年 | 51篇 |
1996年 | 48篇 |
1995年 | 44篇 |
1994年 | 44篇 |
1993年 | 34篇 |
1992年 | 43篇 |
1991年 | 36篇 |
1990年 | 32篇 |
1989年 | 22篇 |
1988年 | 20篇 |
1987年 | 19篇 |
1986年 | 24篇 |
1985年 | 21篇 |
1984年 | 24篇 |
1983年 | 8篇 |
1982年 | 9篇 |
1981年 | 17篇 |
1980年 | 15篇 |
1979年 | 12篇 |
1978年 | 7篇 |
1977年 | 14篇 |
1976年 | 7篇 |
1975年 | 10篇 |
1974年 | 12篇 |
排序方式: 共有3931条查询结果,搜索用时 15 毫秒
11.
SC_9-4是以植物油为原料研制成功的一种高速冷轧工艺润滑油。经武钢高速冷轧机轧制性能鉴定,它的高速轧制性能优于棕榈油。我们使用高效液相色谱比较分析鉴定了SC_9-4和棕榈油的甘油三酯组成。分析结果:SC_9-4:的主要甘油三酯是POP(42.8%)和PPP(14.6%),而棕榈油的主要甘油三酯是POP(31.3%)、POO(20.1%)、PLP(12.2%)和PLO(11.6%)。我们初步探讨甘油三酯组成与轧制性能关系认为,SC_9-4的高速轧制性能优于棕榈油,可能是和SC_9-4含PPP、PPS和PSS的含量(18.8%)高于棕榈油(9.9%)有关。 相似文献
12.
ABSTRACT.
- 1 Larval performance of the leaf beetle Paropsis atomaria Oliver was determined for larvae raised on both new and mature leaves of Eucalyptus blakelyi Maiden. Larvae were transferred to mature leaves at different ages; control larvae stayed on new leaves through all instars.
- 2 Only larvae reared on new leaves through the third instar survived to pupate on mature leaves; developmental time was prolonged by 20% and pupal weight was reduced by 50% in these larvae compared with larvae reared entirely on new leaves. Almost all larvae died when transferred to mature leaves as first, second or third instars.
- 3 Low survival and slow development on mature leaves was mainly due to failure by larvae to feed. Larvae palpated leaves and could discriminate among leaf ages immediately, without biting into the leaf tissue.
- 4 New leaves had higher concentrations of oil and tannins than old leaves, while there were no significant differences in nitrogen concentrations in the two types of leaves. Mature leaves were more than 3 times tougher than new leaves, in terms of g mm?2 of penetrometer force.
- 5 In drought years E. blakelyi may not produce sufficient new leaves to supply specialist herbivores with their preferred food resource. We infer that drought years reduce P. atomaria larval performance significantly, and influence the population dynamics of the insect.
13.
不同季节银木叶精油化学成分的研究 总被引:1,自引:0,他引:1
黄远征;温鸣章;肖顺昌;赵蕙;任维俭 《武汉植物学研究》1988,6(3):253-259
用毛细管气相色谱-质谱-计算机联用技术、毛细管气相色谱双柱保留指数法和双柱标准品叠加法分析了不同季节银木叶精油化学成分。从分离出来的207—250个色谱峰中,初步鉴定出59个成分,被鉴定成分的总量占精油总组成的94.45—98.92%,其主要成分随采油季节不同而有所不同。 相似文献
14.
The growth of mustard was increased significantly when treated with up to 80 kg N ha–1 (N80). Spraying with (2-chloroethyl) trimethylammoniumchloride (chlormequat chloride) increased seed yield and seed protein content. Spraying nitrogen fertilized plots with chlormequat chloride, increased leaf area, leaf area ratio, leaf area duration, number of siliquae plant–1, number of seeds siliqua–1 and length of siliqua. Reducing, non-reducing and total sugars in the leaves at 80 days after sowing were also affected significantly. Chlorophyll a, b and total chlorophyll were little affected. The number of siliquae plant–1 was highly correlated with seed yield in both the seasons of experimentation. The correlation coefficient value () was 0.586 in 1982/83 and 0.912 in 1983/84.The total accumulation of nutrients, i.e. nitrogen, phosphorus and potassium in seed and straw was significantly affected by N80 × chlormequat chloride interaction. 相似文献
15.
The influences of diets having different fatty acid compositions on the fatty-acid content, desaturase activities, and membrane fluidity of rat liver microsomes have been analyzed. Weanling male rats (35–45 g) were fed a fat-free semisynthetic diet supplemented with 10% (by weight) marine fish oil (FO, 12.7% docosahexaenoic acid and 13.8% eicosapentaenoic acid), evening primrose oil (EPO, 7.8% γ-linolenic acid and 70.8% linoleic acid) or a mixture of 5% FO-5% EPO. After 12 weeks on the respective diets, animals fed higher proportions of (n-3) polyunsaturated fatty acids (FO group) consistently contained higher levels of 20:3(n-6), 20:5(n-3), 22:5(n-3), and 22:6(n-3), and lower levels of 18:2(n-6) and 20:4(n-6), than those of the EPO (a rich source of (n-6) polyunsaturated fatty acids) or the FO + EPO groups. Membrane fluidity, as estimated by the reciprocal of the order parameter SDPH, was higher in the FO than in the EPO or the FO + EPO groups, and the n-6 fatty-acid desaturation system was markedly affected. 相似文献
16.
抗寒性不同的油橄榄品种和单株叶片扫描电镜观察 总被引:1,自引:0,他引:1
抗寒性强的油橄榄——克里302、尼基特371的叶片,扫描电镜下的特征是:(1) 近轴表皮角质膜厚,蜡质结晶致密。(2) 远轴表皮内陷气孔,密被鳞毛。(3) 叶两面栅栏组织发达,为旱生形态阳叶结构。 相似文献
17.
神农香菊干花净油成分的研究 总被引:5,自引:2,他引:3
王国亮;王金凤;张红旗;贾卫疆;袁焱明 《武汉植物学研究》1986,4(1):65-68
神农香菊全草提取的香浸膏香气浓郁独特,可用于调配多种高档化妆用香精,也可直接用于饮料中,在香精香料工业中具有较大的实用价值。本文首次报告了我们用毛细管气相色谱仪和色谱/质谱/计算机联用分析仪,对神农香菊干花净油成分进行分析的初步结果。鉴定出的已知成分包括脂肪族类,含氧或非含氧的单萜及倍半萜类化合物32个。 相似文献
18.
19.
Ronald E. Ferrell Ernest D. Seneca Rick A. Linthurst 《Journal of experimental marine biology and ecology》1984,83(1):27-39
Greenhouse studies were conducted to examine the effects of crude oil on the growth of Spartinaalterniflora Loisel. and S. cynosuroides (L.) Roth from North Carolina. The way in which crude oil came into contact with the plant tissue and/or substratum was an important factor in determining the responses of both species to oil pollution. Plants recovered from a single application of oil to aerial tissue with relatively little impact on productivity. The presence of an oil layer on the surface of an overlying layer of water had little impact on existing aerial portions of S. alterniflora plants; however, regrowth following harvest was completely inhibited. Incorporation of oil into the substratum significantly reduced aerial productivity and regrowth of S. alternflora and S. cynosuroides. Observations suggest that decreased productivity and regrowth may have been caused by decreased root and rhizome growth. Regrowth potential of S. alterniflora grown in oiled substratum was greater in fine-textured marsh substratum than in sand substratum. 相似文献
20.
C. P. Malik Usha Parmar Parmil Singh K. L. Ahuja R. K. Raheja 《Plant Growth Regulation》1986,4(2):159-168
Plants of peanut (Arachis hypogaea L. var. PG No. 1) were given two foliar sprays of phenolic compounds (H-acid, 1, 2, 4-acid, resorcinol and RD-Brown) at 100 and 200 ppm, 35 and 50 days after sowing. In treated plants, shelling %, yield (kg/ha), number of gynophores per plant and number of pods per plant were significantly greater than in the control. Oil content of kernels also showed a significant increase with all the phenolic compounds applied. These compounds increased the linoleic acid concentration so improving nutritional quality. The number of gynophores was significantly correlated with the number of pods per plant and yield per hectare. The effect of phenolic compounds on growth and development was independent of their structural configuration. 相似文献