全文获取类型
收费全文 | 2199篇 |
免费 | 184篇 |
专业分类
2383篇 |
出版年
2022年 | 16篇 |
2021年 | 33篇 |
2020年 | 18篇 |
2019年 | 25篇 |
2018年 | 29篇 |
2017年 | 24篇 |
2016年 | 39篇 |
2015年 | 72篇 |
2014年 | 98篇 |
2013年 | 89篇 |
2012年 | 137篇 |
2011年 | 113篇 |
2010年 | 69篇 |
2009年 | 65篇 |
2008年 | 74篇 |
2007年 | 87篇 |
2006年 | 76篇 |
2005年 | 86篇 |
2004年 | 74篇 |
2003年 | 67篇 |
2002年 | 68篇 |
2001年 | 63篇 |
2000年 | 81篇 |
1999年 | 52篇 |
1998年 | 32篇 |
1997年 | 23篇 |
1996年 | 22篇 |
1995年 | 30篇 |
1994年 | 23篇 |
1993年 | 18篇 |
1992年 | 39篇 |
1991年 | 51篇 |
1990年 | 51篇 |
1989年 | 53篇 |
1988年 | 37篇 |
1987年 | 34篇 |
1986年 | 35篇 |
1985年 | 36篇 |
1984年 | 31篇 |
1983年 | 18篇 |
1980年 | 15篇 |
1979年 | 18篇 |
1978年 | 15篇 |
1977年 | 19篇 |
1976年 | 18篇 |
1975年 | 18篇 |
1974年 | 19篇 |
1973年 | 15篇 |
1971年 | 16篇 |
1969年 | 16篇 |
排序方式: 共有2383条查询结果,搜索用时 15 毫秒
1.
E Ortega Rincón J M Marchena J J García A Schmidt T Schulz I Malpica A B Rodríguez C Barriga H Michna H L?tzerich 《Journal of applied physiology》2001,91(3):1067-1072
Flow cytometer measurements were made of the basal variations in peripheral blood functional monocytes and granulocytes over the course of a training season (January to November) of a cycling team. Parallel determinations were made of plasma concentration of catecholamines (chromatography) and cortisol (RIA) in a search for neuroendocrine markers. The results showed the greatest phagocytic capacity to occur in the central months (March, May, and July), coinciding with the greatest number and highest level of competitive events with good correlation with a peak in epinephrine during these months (r(2) = 0.998 for monocytes and r(2) = 0.674 for granulocytes). No good correlations were found between phagocytosis and norepinephrine or cortisol. The highest values for phagocytosis and epinephrine concentration were found in May. These results suggest that blood epinephrine concentration could be a good neuroendocrine marker of sportspeople's phagocytic response. 相似文献
2.
3.
Syee Weldeab Kay-Christian EmeisChristoph Hemleben Gerhard SchmiedlHartmut Schulz 《Palaeogeography, Palaeoclimatology, Palaeoecology》2003,191(2):169-190
We investigated five time-equivalent core sections (180-110 kyr BP) from the Balearic Sea (Menorca Rise), the easternmost Levantine Basin and southwest, south, and southeast of Crete to reconstruct spatial patterns of productivity during deposition of sapropels S5 and S6 in the Mediterranean Sea. Our indicators are Ba, total organic carbon and carbonate contents. We found no indications of Ba remobilization within the investigated core intervals, and used the accumulation rate of biogenic Ba to compute paleoproductivity. Maximum surface water productivity (up to 350 g C/m2/yr) was found during deposition of S5 (isotope stage 5e) but pronounced spatial variability is evident. Coeval sediment intervals in the Balearic Sea show very little productivity change, suggesting that chemical and biological environments in the eastern and western Mediterranean basins were decoupled in this interval. We interpret the spatial variability as the result of two different modes of nutrient delivery to the photic zone: river-derived nutrient input and shoaling of the pycnocline/nutricline to the photic zone. The productivity increase during the formation of S6 was moderate compared to S5 and had a less marked spatial variability within the study area of the eastern Mediterranean Sea. Given that S6 formed during a glacial interval, glacial boundary conditions such as high wind stress and/or cooler surface water temperatures apparently favored lateral and vertical mixing and prevented the development of the spatial gradients within the Eastern Mediterranean Sea (EMS) observed for S5. A non-sapropel sediment interval with elevated Ba content and depleted 18O/16O ratios in planktonic foraminifer calcite was detected between S6 and S5 that corresponds to the weak northern hemisphere insolation maximum at 150 kyr. At this time, productivity apparently increased up to five times over surrounding intervals, but abundant benthic fauna show that the deep water remained oxic. Following our interpretation, the interval denotes a failed sapropel, when a weaker monsoon did not force the EMS into permanent stratification. The comparison of interglacial and glacial sapropels illustrates the relevance of climatic boundary conditions in the northern catchment in determining the facies and spatial variability of sapropels within the EMS. 相似文献
4.
Sixteen raptors, including one eagle, two falcons, five hawks and eight owls, were found to have developmental ocular lesions. The most common lesion was microphthalmia. Other findings included cataract, microphakia, retinal dysplasia, malformation of the ciliary body, choroid and pecten, and lentoid formation. Specific causes for these lesions could not be determined. It is hypothesized that developmental ocular disease probably is more common than available reports indicate. 相似文献
5.
6.
7.
A. Schulz 《Protoplasma》1986,130(1):12-26
Summary 48 hours after interrupting the root stele ofPisum, wound phloem initiated (proximally or distally to the wound) to reconnect the vascular stumps was found to contain some nucleate wound-sieve elements. At the elongating end of an incomplete wound-sieve tube these elements exhibit a sequence of ultrastructural changes as known from protophloem-sieve tubes. Elongation occurs by the addition of newly divided (wound-) sieve-element/companion-cell complexes. In order to dedifferentiate and assume a new specialization formerly quiescent stelar or cortical cells require at least one (mostly more) preliminary division. Companion cells are consequently obligatory sister cells to wound-sieve elements.By reconstruction using serial sections it could be shown that wound-sieve tubes elongate bidirectionally, starting in an early activated procambial cell of the stele. The elongation is directed by the existence of plasmodesmata, preferably when lying in primary pit fields, and by the plane of preceding divisions. Thus, the developing wound-sieve tube can deviate from the damaged bundle and radiate into the cortex as soon as the plane of the preceding divisions is favourable. In the opposite direction, elongating wound-sieve tubes run parallel to pre-existing phloem traces, thus broading their base at the bundle for the deviating part of the wound-sieve tube. Frequently an individual wound-sieve tube is supplemented at the bundle by a further wound-sieve tube which is partly running parallel to it. Both sieve tubes are interlinked with sieve plates by three-poled sieve elements.Ultrastructurally, the developmental changes of nucleate wound-sieve elements follow the known pattern. In spite of its contrasting origin and odd shape a mature wound-sieve element eventually has the same contents as regular sieve elements: sieve-element plastids, mitochondria, stacked ER and small amounts of P-protein within an electronlucent cytoplasm. 相似文献
8.
R Smith R R Preston S Schulz M L Gagnon J Van Houten 《Biochimica et biophysica acta》1987,928(2):171-178
Paramecium tetraurelia is attracted to cyclic AMP, which probably, as other attractants, signifies the presence of food. Attraction to cyclic AMP was specific, saturable, and, therefore, likely to be receptor-mediated. In these studies, we measured the binding of cyclic [3H]AMP to whole cells and found it to be saturable, reversible, and displaying specificity similar to that of attraction. An HPLC method of separating nucleotides was devised and used to determine that external cyclic AMP was degraded in the absence of IBMX, a phosphodiesterase inhibitor, and that cyclic AMP was taken into the cells in small amounts. Since binding and attraction were subsequently measured in the presence of IMBX, it was cyclic AMP and not a degradation product that served as the attractant stimulus for Paramecium. 相似文献
9.
The effects of a single post-trial intraperitoneal administration of the dipeptide Litoralon (gamma-L-glutamyl-taurine) and some of its analogues were tested on the passive avoidance latency of male and female Wistar rats. The avoidance latency was significantly decreased by Litoralon and gamma-aminobutyryl-ethanolamine phosphate but lengthened by DL-beta-aminoisobutyryl-ethanolamine phosphate. No differences were observed between the responses of immature male and female rats following Litoralon treatment. The observed inter-group differences in passive avoidance behaviour following dipeptide administration were also demonstrable in tests of the open-field activity of the animals examined immediately after the 24-hour retention test. The results are discussed on the basis of a central Litoralon effect on emotional arousal and the anti-conflict potencies of the dipeptide. 相似文献