全文获取类型
收费全文 | 1914篇 |
免费 | 89篇 |
国内免费 | 5篇 |
专业分类
2008篇 |
出版年
2023年 | 13篇 |
2022年 | 38篇 |
2021年 | 42篇 |
2020年 | 32篇 |
2019年 | 37篇 |
2018年 | 58篇 |
2017年 | 51篇 |
2016年 | 68篇 |
2015年 | 96篇 |
2014年 | 119篇 |
2013年 | 152篇 |
2012年 | 150篇 |
2011年 | 142篇 |
2010年 | 96篇 |
2009年 | 84篇 |
2008年 | 85篇 |
2007年 | 86篇 |
2006年 | 85篇 |
2005年 | 59篇 |
2004年 | 74篇 |
2003年 | 52篇 |
2002年 | 37篇 |
2001年 | 30篇 |
2000年 | 25篇 |
1999年 | 27篇 |
1998年 | 18篇 |
1997年 | 11篇 |
1996年 | 7篇 |
1995年 | 7篇 |
1994年 | 6篇 |
1993年 | 7篇 |
1992年 | 10篇 |
1991年 | 25篇 |
1990年 | 13篇 |
1989年 | 16篇 |
1988年 | 10篇 |
1987年 | 11篇 |
1986年 | 17篇 |
1985年 | 14篇 |
1984年 | 22篇 |
1983年 | 14篇 |
1982年 | 10篇 |
1981年 | 11篇 |
1980年 | 7篇 |
1979年 | 3篇 |
1978年 | 6篇 |
1976年 | 4篇 |
1975年 | 6篇 |
1972年 | 4篇 |
1968年 | 2篇 |
排序方式: 共有2008条查询结果,搜索用时 0 毫秒
11.
G Tripathi 《The Journal of experimental zoology》1984,232(1):151-155
Administration of estradiol dipropionate (20 micrograms/day; 7 days) to ovariectomized mice caused heavy epithelial proliferation and intense cornification in the vagina and cellular as well as glandular proliferation in uterine tissues. Endometrial hypertrophy with cystlike appearance of uterine glands was seen in response to a long-term (14 days) administration of estradiol dipropionate. Daily injection of progesterone (2 mg; 7 days) to ovariectomized mice resulted in desquamating mucosa, without any trace of vaginal cornification, and the presence of dense uterine connective tissue in the stromal region with typical uterine glands. However, treatment of estradiol depropionate in combination with progesterone at 1:100 dose ratio for 7 days produced vaginal histology similar to that in proestrus and uterine histology equivalent to the ovariectomized condition. The results revealed that progesterone antagonized the estrogenic effects and also that estradiol dipropionate antagonized the effects of progesterone. The effects of the two female sex steroids (estradiol dipropionate and progesterone) in vivo appeared to be more potent in the uterus than in the vagina. 相似文献
12.
The essential oil from the fruits of Trachyspermum ammi exhibited toxicity at 800 ppm against Aspergillus flavus and A. niger, the nature of toxicity being cidal. The toxicity of the oil was not affected by autoclaving, temperature treatment and storage upto 365 days. The oil killed the test fungi within 50 seconds; withstood heavy inoculum density and was inhibitory to as many as 21 fungi at its minimum inhibitory concentration. However the seeds of Arachis hypogea whentreated with oil at 5000 ppm and stored for 12 months did not show the appearance of any fungi indicating thereby the grain protectant activity of the oil. The oil was characterized by various physico chemical properties and on chemical investigation Thymol and p-cymene were isolated as antifungal principles of the oil exhibiting toxicity against the test fungi at 1000 ppm. 相似文献
13.
Tilletia indica teliospores were studied by use of thin sections and freeze-etch replicas. Surfaces of these spores have rodlet patterns which differ from those previously reported for spores of other fungi. The rodlets on T. indica teliospores average 240 nm in length and are not grouped into fascicles. 相似文献
14.
Composition of complex lipid of chloroplasts of two cultivars of wheat and barley was determined at tillering, ear emergence and grain filling stages. The chloroplast lipids, MGDG, DGDG and PG were maximum at grain filling stage in both wheat and barley. PC content showed variations at different stages in both the crops while no significant changes were observed in PI concentrations at grain filling stage. 相似文献
15.
Study of the gametocytocidal/sporontocidal action of qinghaosu (artemisinin) by electron microscopy 总被引:1,自引:0,他引:1
The gametocytocidal efficacy of artemisinin (qinghaosu) was evaluated and scanning electron microscopical evidence is given for gametocytocidal action of a single 5-10-mg/kg dose of artemisinin against simian malarial parasite (Plasmodium cynomolgi B). No sporontocidal effect of artemisinin was observed. 相似文献
16.
A life-table was constructed for a little known aphidiid waspLysiphlebia mirzai, a parasitoid of cereal aphid,Rhopalosiphum maidis. The female parasitoid survived 6.4 ± 1.17 (SD) days and oviposited intensively 4.0 ± 0.47 days. The total fecundity rate,
Rt, was 169.2 ± 6.94 mummies/female and net reproductive rate, Ro, was 92.70 female offspring/female. The intrinsic total fecundity rate, rt, and intrinsic rate of natural increase, rm, the finite rate of total fecundity, λt, and finite rate of increase, λm, was 0.27048, 0.24155, 1.31059 and 1.27322 respectively. The mean generation time (18.75 days) and doubling time of the population
(2.87 days) was slightly higher than other aphidiids studied so far. The proportion of female progenies decreased significantly
on the successive oviposition days.
相似文献
17.
Cropping on jhum fallows in north-eartern India is predominantly done for one year in a jhum cycle. If second year cropping
is done, expanse of the forest land required for slashing and burning could be reduced significantly. We tested this hypothesis
in a young (6 yr) and an old (20 yr) jhum fallow. We also evaluated if the productivity during second year cropping could
be alleviated by auxiliary measures such as tilling the soil or application of fertilizers (chemical or farm-yard manure or
both in combination). The results demonstrate that the ecosystem productivity (total dry matter production) and economic yield
(rice grain production) decline with shortening of jhum cycle. Second year cropping causes a further decline in ecosystem
productivity in old jhum field, but not in young jhum field. Economic yield from second year cropping in its traditional form
(without any fertilizer treatment) is not much lower than that in the first year, and can be improved further by manuring
the soil. Tilling of soil improves neither ecosystem productivity nor economic yield. Different fertilization treatments respond
differently; while inorganic manuring enhances ecosystem productivity, a combination of inorganic and organic manuring improves
economic yield 相似文献
18.
The transforming growth factor beta type II receptor can replace the activin type II receptor in inducing mesoderm. 总被引:3,自引:0,他引:3
下载免费PDF全文
![点击此处可从《Molecular and cellular biology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
The type II receptors for the polypeptide growth factors transforming growth factor beta (TGF-beta) and activin belong to a new family of predicted serine/threonine protein kinases. In Xenopus embryos, the biological effects of activin and TGF-beta 1 are strikingly different; activin induces a full range of mesodermal cell types in the animal cap assay, while TGF-beta 1 has no effects, presumably because of the lack of functional TGF-beta receptors. In order to assess the biological activities of exogenously added TGF-beta 1, RNA encoding the TGF-beta type II receptor was introduced into Xenopus embryos. In animal caps from these embryos, TGF-beta 1 and activin show similar potencies for induction of mesoderm-specific mRNAs, and both elicit the same types of mesodermal tissues. In addition, the response of animal caps to TGF-beta 1, as well as to activin, is blocked by a dominant inhibitory ras mutant, p21(Asn-17)Ha-ras. These results indicate that the activin and TGF-beta type II receptors can couple to similar signalling pathways and that the biological specificities of these growth factors lie in their different ligand-binding domains and in different competences of the responding cells. 相似文献
19.
Mutations of the tyrosinase gene in patients with oculocutaneous albinism from various ethnic groups in Israel. 总被引:5,自引:0,他引:5
下载免费PDF全文
![点击此处可从《American journal of human genetics》网站下载免费的PDF全文](/ch/ext_images/free.gif)
R. Gershoni-Baruch A. Rosenmann S. Droetto S. Holmes R. K. Tripathi R. A. Spritz 《American journal of human genetics》1994,54(4):586-594
We have analyzed the tyrosinase (TYR) gene in 38 unrelated patients with oculocutaneous albinism (OCA), derived from several different ethnic groups of the diverse population of Israel. We detected TYR gene mutations in 23 of the 34 patients with apparent type I (i.e., tyrosinase-deficient) OCA and in none of the patients with other clinical forms of albinism. Among Moroccan Jews with type IA (i.e., tyrosinase-negative) OCA, we detected a highly predominant mutant allele containing a missense substitution, Gly47Asp (G47D). This mutation occurs on the same haplotype as in patients from the Canary Islands and Puerto Rico, suggesting that the G47D mutation in these ethnically distinct populations may stem from a common origin. 相似文献
20.
Fourier transform infrared spectroscopy is used to characterize specific interactions between negatively charged lipids, such as phosphatidic acid, and the purified nicotinic acetylcholine receptor from Torpedo californica. The specific interaction of phosphatidic acid with acetylcholine receptor is demonstrated by the receptor-induced perturbation of the lipid ionization state, which is monitored using Fourier transform infrared bands arising from the phosphate head group. The acetylcholine receptor shifts the pKa of phosphatidic acid molecules adjacent to the receptor to a lower value by almost 2 pH units from 8.5 to 6.6. Decreased pH also leads to changes in ion channel function and to changes in the secondary structure of the acetylcholine receptor in membranes containing ionizable phospholipids. Phospholipase D restores functional activity of acetylcholine receptor reconstituted in an unfavorable environment containing phosphatidylcholine by generating phosphatidic acid. Lipids such as phosphatidic acid may serve as allosteric effectors for membrane protein function and the lipid-protein interface could be a site for activity-dependent changes that lead to modulation of synaptic efficacy. 相似文献