全文获取类型
收费全文 | 927篇 |
免费 | 56篇 |
国内免费 | 3篇 |
专业分类
986篇 |
出版年
2024年 | 1篇 |
2023年 | 15篇 |
2022年 | 31篇 |
2021年 | 62篇 |
2020年 | 26篇 |
2019年 | 27篇 |
2018年 | 29篇 |
2017年 | 25篇 |
2016年 | 63篇 |
2015年 | 42篇 |
2014年 | 70篇 |
2013年 | 66篇 |
2012年 | 70篇 |
2011年 | 73篇 |
2010年 | 32篇 |
2009年 | 38篇 |
2008年 | 50篇 |
2007年 | 35篇 |
2006年 | 26篇 |
2005年 | 35篇 |
2004年 | 41篇 |
2003年 | 21篇 |
2002年 | 28篇 |
2001年 | 4篇 |
2000年 | 15篇 |
1999年 | 5篇 |
1998年 | 2篇 |
1997年 | 3篇 |
1996年 | 2篇 |
1995年 | 2篇 |
1994年 | 3篇 |
1993年 | 4篇 |
1992年 | 2篇 |
1991年 | 7篇 |
1990年 | 2篇 |
1989年 | 6篇 |
1988年 | 2篇 |
1987年 | 2篇 |
1986年 | 2篇 |
1985年 | 1篇 |
1984年 | 5篇 |
1983年 | 1篇 |
1981年 | 2篇 |
1979年 | 1篇 |
1977年 | 2篇 |
1973年 | 2篇 |
1972年 | 2篇 |
1960年 | 1篇 |
排序方式: 共有986条查询结果,搜索用时 0 毫秒
1.
2.
Application of phosphorus at 40, 60, 80 and 100 kg P2O5 ha–1 in the presence of a uniform dressing of nitrogen (N) and potash (K2O) each applied at 20 and 24 kg ha–1 to chickpea (CM-88) grown in sandy loam soil in a replicated field experiment improved the nodulation response of the crop, increased its grain yield (ka ha–1) by 18, 59, 40 and 14 percent, biomass yield (ka ha–1) by 32, 32, 54 and 14 percent, biomass N (kg ha–1) by 31, 48, 49, 19 percent, and biomass P (kg ha–1) by 26, 40, 41 and 11 percent, respectively. The effect of phosphorus on the nitrogenase activity of the excised roots of chickpea was, however, inconsistent. 相似文献
3.
Summary Mutant strains were derived from Clostridium thermoaceticum ATCC 39 289 by treatment with chemical mutagenic agents and selective enrichment procedures. Some mutant strains exhibited growth when cultured in media containing 20 mabetm (1.75 g l–1) pyruvate of high-magnesium lime (dolime) above pH 6.0. One strain (G-20) grew and produced acetate when 80 mabetm (7 gl–1) pyruvate or 50 mabetm (2.3 g l–1) formate at pH 5.6 was the sole energy source. In a fed-batch process controlled at pH 6.2, this mutant produced 52.5 g l–1 acetate (equivalent to 72.5 g l–1 Na acetate) and 67 g l–1 calcium-magnesium acetate (CMA) in 140 h when dolime was the neutralizing agent, with 93% substrate utilization. This mutant strain holds promise for CMA production due to its better tolerance of dolime and its ability to synthesize high levels of acetic acid.
Offprint requests to: S. R. Parekh 相似文献
4.
The effect of bromocriptine, a dopamine receptor agonist, has been studied on the aspirin, phenylbutazone and reserpine induced gastric ulcers in rats. A single dose of bromocriptine 4 mg/kg s.c. produced a significant exacerbation of gastric ulcers induced by all the three ulcerogenic drugs, whereas in the same dose administered once daily for 5 consecutive days, it produced a marked protective effect in all the models. A review of the literature shows that different mechanisms may be involved in the opposite effects of acutely and chronically administered bromocriptine observed in this study. The study also points towards a role of dopamine in the pathogenesis of gastroduodenal ulceration. 相似文献
5.
The effect of cathinone and amphetamine on brown adipose tissue thermogenesis and its modification with propranolol and timolol has been studied in rats. Both cathinone and amphetamine produced significant dose dependent increases in intracapsular brown adipose tissue (IBAT) and rectal temperatures. Amphetamine was found to be three times more potent as compared to cathinone, on a dose basis. Pretreatment of animals with propranolol and timolol individually inhibited cathinone and amphetamine induced hyperthermia. These findings suggest the involvement of beta adrenergic receptors in cathinone and amphetamine induced thermogenesis. 相似文献
6.
Soraya C. M. Leal David J. Bertioli Brenda V. Ball Tariq M. Butt 《Biocontrol Science and Technology》1994,4(1):89-94
Nucleic acids from 41 strains of Metarhizium anisopliae, obtained from different parts of the world were extracted and examined by electrophoresis. Strong bands of double‐stranded RNA (dsRNA) were detected in two isolates from Brazil, V215 and V291, which had, respectively, 13 and 9 distinct bands ranging in size from ca. 0.75 to 3.5 kb. Icosahedral virus‐like particles (VLPs) (ca. 33 nm in diameter) were observed by transmission electron microscopy in extracts of these isolates. The VLPs and dsRNA were both absent from a clone of the isolate V291 which had been subcultured successively on solid medium. Bioassays against the aphid Myzus persicae showed no detectable difference in virulence between the clone of V291 which contained dsRNA and the clone that did not. 相似文献
7.
Tianyuan Li Saif Ullah He Liang Izhar Ali Quan Zhao Anas Iqbal Shanqing Wei Tariq Shah Yuqiong Luo Ligeng Jiang 《Phyton》2021,90(1):223-243
Readily available chemical fertilizers have resulted in a decline in the
use of organic manure (e.g., green manures), a traditionally sustainable source
of nutrients. Based on this, we applied urea at the rate of 270 kg ha−1 with and
without green manure in order to assess nitrogen (N) productivity in a double rice
cropping system in 2017. In particular, treatment combinations were as follows:
winter fallow rice-rice (WF-R-R), milk vetch rice-rice (MV-R-R), oil-seed rape
rice-rice (R-R-R) and potato crop rice-rice (P-R-R). Results revealed that green
manure significantly (p ≤ 0.05) improved the soil chemical properties and net soil
organic carbon content increased by an average 117.47%, total nitrogen (N) by
28.41%, available N by 26.64%, total phosphorus (P) by 37.77%, available P
by 20.48% and available potassium (K) by 33.10% than WF-R-R, however pH
was reduced by 3.30% across the seasons. Similarly, net dry matter accumulation
rate enhanced in green manure applied treatments and ranked in order: P-R-R >
R-R-R > MV-R-R > WF-R-R. Furthermore, the total leaf dry matter transport
(t ha−1
) for the P-R-R in both seasons was significantly higher by an average
11.2%, 7.2% and 36 % than MV-R-R, R-R-R, and WF-R-R, respectively. In addition, net total nitrogen accumulation (kg ha−1
) was found higher in green manure
applied plots compared to the control. Yield and yield attributed traits were
observed maximum in green manure applied plots, with treatments ranking as follows: P-R-R > R-R-R > MV-R-R > WF-R-R. Thus, results obtained highlight
ability of green manure to sustainably improve soil quality and rice yield. 相似文献
8.
Expression of desmin, laminin and fibronectin during in situ differentiation (decidualization) of rat uterine stromal cells 总被引:2,自引:0,他引:2
Stanley R. Glasser Saara Lampelo M. Idrees Munir JoAnne Julian 《Differentiation; research in biological diversity》1987,35(2):132-142
Immunocytochemical analysis of frozen rat uterine sections containing decidual tissue, formed in response to normal or artificial stimulation of uteri sensitized by endogenous or exogenous hormonal regimens, demonstrated an elevated expression of the intermediate filament protein desmin in decidual cells. Changes in the expression of extracellular matrix (ECM) components were coordinated with the elevated expression of desmin as stromal cells underwent decidualization. In parallel with the pattern of regional decidualization, as determined by elevated desmin expression, laminin accumulated in ECM of decidual cells while an apparent decrease in fibronectin was associated with altered organization at the decidual cell surface. The in situ observations confirm previous results, which indicated that the expression of desmin in decidual cells formed in vivo or in vitro is a valid marker of their differentiation, and resolve questions unanswered in the previous study: (a) desmin (and laminin) appear to be constitutively expressed in non-decidualized stroma at barely detectable levels, (b) desmin is a valid marker of stromal cell differentiation because it is expressed similarly in decidual cells, irrespective of varying experimental protocols for uterine sensitization and stimulation, and (c) desmin expression follows the same regional progression described for the process of decidualization in morphological and histochemical studies. 相似文献
9.
10.
Mated male Argas persicus were dissected 1 and 2 weeks after feeding on untreated and ivermectin (IVM)-treated pigeons. One week after feeding, testes of untreated ticks were filled with rounded spermatids with subplasmalemmal vesicles and cytoplasmic organelles, but lacking in treated ticks. Two weeks after feeding, testes were crowded with elongated spermatozoa supported by double-walled cisternal tubes. The tubes consisted of two opposite walls, each with outer-fringed processes and inner elongated cisternae. Both were supported with electron dense striated plates in the middle of the spermatozoon. Internally, the cisternal tubes contained mitochondria and vacuoles. The nuclei were elongated dense masses between the tubes and the cell membranes. Subcutaneous inoculation of IVM at the dose 400 μg/kg pigeon resulted in extensive alterations in the testis of A. persicus. IVM prevented the development of new spermatids. There was a break down of cell membranes and cytoplasmic organelles of spermatozoa. Multivesicular bodies and numerous vacuoles were noticed in their cytoplasm. Double membranes of elongated cisternae and striation of electron dense plates became indistinct. IVM caused granulation and vacuolization of the nucleus as well as injury of mitochondrial cristae. The results suggest that IVM may bind to the neurotransmitter or the hormone involved in the process of sperm development or may be toxic to the germinal cells of A. persicus testis. 相似文献