全文获取类型
收费全文 | 2977篇 |
免费 | 253篇 |
出版年
2023年 | 13篇 |
2022年 | 24篇 |
2021年 | 68篇 |
2020年 | 23篇 |
2019年 | 53篇 |
2018年 | 60篇 |
2017年 | 47篇 |
2016年 | 109篇 |
2015年 | 171篇 |
2014年 | 211篇 |
2013年 | 242篇 |
2012年 | 330篇 |
2011年 | 253篇 |
2010年 | 201篇 |
2009年 | 136篇 |
2008年 | 200篇 |
2007年 | 188篇 |
2006年 | 160篇 |
2005年 | 158篇 |
2004年 | 144篇 |
2003年 | 117篇 |
2002年 | 119篇 |
2001年 | 31篇 |
2000年 | 13篇 |
1999年 | 21篇 |
1998年 | 17篇 |
1997年 | 14篇 |
1996年 | 13篇 |
1995年 | 22篇 |
1994年 | 7篇 |
1993年 | 12篇 |
1992年 | 12篇 |
1991年 | 9篇 |
1990年 | 8篇 |
1989年 | 2篇 |
1988年 | 4篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1982年 | 4篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1977年 | 2篇 |
1976年 | 2篇 |
1975年 | 1篇 |
1974年 | 1篇 |
排序方式: 共有3230条查询结果,搜索用时 15 毫秒
11.
Prediction of the Reaction Equilibrium of Biocatalytic Reactions in Aqueous-Organic Two-Phase Systems 总被引:1,自引:0,他引:1
Anja E. M. Janssen Albert Van Der Padt Klaas Van't Riet 《Biocatalysis and Biotransformation》1995,12(4):223-240
Biocatalytic reactions can be carried out in aqueous-organic two-phase systems. Several models to describe the thermodynamically-determined equilibrium position in such systems have appeared in the literature. Some of these models are only valid for dilute systems, whereas others can also be used for nondilute systems. In this paper, these models are described and compared. It is explained in what way the equilibrium constants of each model can be used to predict the product concentration in different organic solvents. 相似文献
12.
Anastassia M. Makarieva Andrei V. Nefiodov Antonio Donato Nobre Mara Baudena Ugo Bardi Douglas Sheil Scott R. Saleska Ruben D. Molina Anja Rammig 《Global Change Biology》2023,29(9):2536-2556
The terrestrial water cycle links the soil and atmosphere moisture reservoirs through four fluxes: precipitation, evaporation, runoff, and atmospheric moisture convergence (net import of water vapor to balance runoff). Each of these processes is essential for sustaining human and ecosystem well-being. Predicting how the water cycle responds to changes in vegetation cover remains a challenge. Recently, changes in plant transpiration across the Amazon basin were shown to be associated disproportionately with changes in rainfall, suggesting that even small declines in transpiration (e.g., from deforestation) would lead to much larger declines in rainfall. Here, constraining these findings by the law of mass conservation, we show that in a sufficiently wet atmosphere, forest transpiration can control atmospheric moisture convergence such that increased transpiration enhances atmospheric moisture import and results in water yield. Conversely, in a sufficiently dry atmosphere increased transpiration reduces atmospheric moisture convergence and water yield. This previously unrecognized dichotomy can explain the otherwise mixed observations of how water yield responds to re-greening, as we illustrate with examples from China's Loess Plateau. Our analysis indicates that any additional precipitation recycling due to additional vegetation increases precipitation but decreases local water yield and steady-state runoff. Therefore, in the drier regions/periods and early stages of ecological restoration, the role of vegetation can be confined to precipitation recycling, while once a wetter stage is achieved, additional vegetation enhances atmospheric moisture convergence and water yield. Recent analyses indicate that the latter regime dominates the global response of the terrestrial water cycle to re-greening. Evaluating the transition between regimes, and recognizing the potential of vegetation for enhancing moisture convergence, are crucial for characterizing the consequences of deforestation as well as for motivating and guiding ecological restoration. 相似文献
13.
14.
Pollen tubes of Nicotiana tabacum and Petunia hybrida show pulsatory growth. Phases of slow growth lasting minutes are interrupted by pulse-like elongations lasting 10–20 seconds involving an increase of growth rate by up to 24-fold. Inhibition of dictyosome activity with brefeldin A or monensin did not result in an inhibition of pulsatory growth but eventually stopped pollen tube elongation. In contrast to this the inhibition of the cytoskeletal elements with cytochalasin D and colchicine caused the pollen tubes to abandon the pulse-like elongations. It was concluded that the activity of the dictyosomes does not have a controlling function in the mechanism of pulsatory growth, even though it is necessary for pollen tube elongation, since cell wall material is provided by secretory vesicles deriving from the Golgi apparatus. In contrast the cytoskeletal elements, actin and microtubules, seem to play an important regulatory role in the pulse-like elongations. In addition, it was observed that during the experiments several pollen tubes burst upon the completion of a pulse-like expansion, indicating on the one hand that the internal turgor is the driving force of the pulse-like expansions. On the other hand, the bursting shows that the pollen tube cell wall is rather weak at the end of a pulse, indicating that at this point of time it is either thinner or less stable than during the slow growth phase or at the beginning of a pulse. 相似文献
15.
Summary The monoclonal antibody (MAb) JIM5, marking acidic pectins, was used to localize ultrastructurally pectin molecules in the pollen tube wall ofNicotiana tabacum. Longitudinal sections of LR-White embedded pollen tubes were exposed to antibody treatment; accumulations of pectins were identified by counting the density of the gold particles representing the pectin epitopes along the pollen tube wall. Significant accumulations of gold grains were marked and the distances between them were measured. In many pollen tubes a more or less regular distribution of the accumulations was observed along the tube indicating a periodical deposition of pectin. The distances between the accumulations were 4–6 m. Most of the label was found in the inner part of the outer layer of the bilayered cell wall. These findings correspond to and confirm the earlier observation by our group reporting ring-shaped periodical deposits in pollen tubes after immunofluorescence labelling with the MAb JIM5 under the confocal laser scanning microscope.Abbreviations Ab
antibody
- MAb
monoclonal antibody 相似文献
16.
17.
Tests testosterone reserve capacity of 6--15 year-old boys was estimated after operative correction of testicular maldescensus by a maximal stimulation test. Subnormal plasma testosterone levels were found in only 2 out of 14 patients with bilateral and 4 with unilateral orchidopexy. Prepubertal boys with unilateral anorchia had normal basal testosterone values and a normal testosterone rise after stimulation. In prepubertal boys with bilateral testes atrophy there was observed a diminished rise after stimulation. The basal testosterone levels were normal. The testosterone basal levels of pubertal boys with unilateral anorchia or bilateral atrophy were subnormal and the stimuation of testosterone production was reduced. The testicular volume of patients without atrophy or anorchia after orchidopexy was normal in prepuberty. During puberta a progressive relative decrease of the testicular volume was observed as compared to normal development. In conclusion, the results demonstrate that the endocrine function in most patients with unilateral or bilateral orchidopexy is in the normal range--a regular puberty can be expected. 相似文献
18.
The effect of methane oxidation in aerobic sediment on oxygen consumption and phosphate flux was investigated in diffusion chambers. The diffusion chambers consisted of two compartments separated by a Teflon membrane. In the upper chamber a thin sediment layer was present and the lower chamber was continuously flushed with gas. The hydrophobic membrane allowed for diffusion of gases from the lower chamber through the sediment layer toward the headspace of the upper chamber. In experiments with a methane oxidation rate of 9.8 mmol m–2 day–1, the oxygen consumption rate increased by a factor of two compared with controls without methane oxidation (8.6 vs 17.7 mmol m–2 day–1). Methane oxidation significantly decreased oxygen penetration depth (2.5–4.0 vs 1.0–2.0 mm). However, despite the shrinkage of the oxidized microlayer, no differences were found in phosphate flux across the sediment water interface. Batch experiments with standard additions of methane revealed that the growth of methanotrophic bacteria contributes to the phosphate uptake of aerobic sediment. From the batch experiments a molar ratio of carbon to phosphate of 45 mol:mol was calculated for the growth of methanotrophs. Results suggest that a decrease in chemical phosphate adsorption caused by a decrease in the oxygen penetration depth could be compensated for entirely by the growth of methanotrophic bacteria.
Send offprint requests to: A.J.C. Sinke 相似文献
19.
A locus for familial hypertrophic cardiomyopathy is closely linked to the cardiac myosin heavy chain genes, CRI-L436, and CRI-L329 on chromosome 14 at q11-q12 总被引:10,自引:1,他引:9 下载免费PDF全文
Scott D. Solomon Anja A. T. Geisterfer-Lowrance Hans-Peter Vosberg Gudrun Hiller John A. Jarcho Cynthia C. Morton Wesley O. McBride Anna L. Mitchell Allen E. Bale William J. McKenna J. G. Seidman Christine E. Seidman 《American journal of human genetics》1990,47(3):389-394
We report that a gene responsible for familial hypertrophic cardiomyopathy (HC) is closely linked to the cardiac alpha and beta myosin heavy chain (MHC) genes on chromosome 14q11. We have recently shown that probe CRI-L436, derived from the anonymous DNA locus D14S26, detects a polymorphic restriction fragment that segregates with familial HC in affected members of a large Canadian family. Using chromosomal in situ hybridization, we have mapped CRI-L436 to chromosome 14 at q11-q12. Because the cardiac MHC genes also map to this chromosomal band, we have determined the genetic distances between the cardiac beta MHC gene, D14S26, and the familial HC locus. Data presented here show that these three loci are linked within 5 centimorgans on chromosome 14 at q11-q12. The possibility that defects in either the cardiac alpha or beta MHC genes are responsible for familial HC is discussed. 相似文献
20.
Intracellular transport in plant cells occurs on microtubular and actin arrays. Cytoplasmic streaming, the rapid motion of plant cell organelles, is mostly driven by an actin–myosin mechanism, whereas specialized functions, such as the transport of large cargo or the assembly of a new cell wall during cell division, are performed by the microtubules. Different modes of transport are used, fast and slow, to either haul cargo over long distances or ascertain high-precision targeting, respectively. Various forms of the actin-specific motor protein myosin XI exist in plant cells and might be involved in different cellular functions. 相似文献