全文获取类型
收费全文 | 379篇 |
免费 | 10篇 |
国内免费 | 53篇 |
出版年
2023年 | 2篇 |
2022年 | 8篇 |
2021年 | 17篇 |
2020年 | 9篇 |
2019年 | 11篇 |
2018年 | 3篇 |
2017年 | 10篇 |
2016年 | 15篇 |
2015年 | 15篇 |
2014年 | 14篇 |
2013年 | 20篇 |
2012年 | 19篇 |
2011年 | 19篇 |
2010年 | 14篇 |
2009年 | 21篇 |
2008年 | 16篇 |
2007年 | 17篇 |
2006年 | 25篇 |
2005年 | 12篇 |
2004年 | 20篇 |
2003年 | 18篇 |
2002年 | 14篇 |
2001年 | 5篇 |
2000年 | 6篇 |
1999年 | 7篇 |
1998年 | 7篇 |
1997年 | 11篇 |
1996年 | 5篇 |
1995年 | 4篇 |
1994年 | 2篇 |
1993年 | 6篇 |
1992年 | 3篇 |
1991年 | 5篇 |
1990年 | 1篇 |
1989年 | 3篇 |
1988年 | 6篇 |
1987年 | 3篇 |
1986年 | 5篇 |
1985年 | 2篇 |
1984年 | 4篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1980年 | 8篇 |
1979年 | 9篇 |
1978年 | 6篇 |
1977年 | 7篇 |
1976年 | 3篇 |
1975年 | 1篇 |
1973年 | 1篇 |
排序方式: 共有442条查询结果,搜索用时 703 毫秒
1.
Peter Lewis 《Journal of bioethical inquiry》2007,4(1):51-55
The display of personal photographs in hospital is a common practice that has yet to be rigorously examined. The photographs
displayed are subject to interpretation by the viewer and may lead to misunderstandings or miscommunication if clarification
of meaning is not sought. This paper explores a range of possible meanings that the display of photographs in hospital may
hold, based on a case study of a 15 year old boy hospitalised with a life threatening illness. Further research is needed
into the actual meanings attributed to the display of photographs in hospital by patients and family members. 相似文献
2.
Juniperus deltoides R.P.Adams is a prickly, evergreen shrub that grows in the East Mediterranean on dry hills and mountains. Needle-like leaves have a thick cuticular layer on the surface, which serves as the ultimate barrier for prevention of water loss. n-Alkanes comprise the biggest part of this hydrophobic wax mixture. These compounds are studied as chemophenetic characters due to their chemical and physiological stability, and strong genetic control. Six central Balkan populations were studied and compared to one eastern and one western. Fifteen n-alkanes were identified, with C33 being dominant in all samples. Univariate and multivariate statistical analyses separated western population from all central Balkan populations, while the eastern Balkan population showed high similarity with the central ones. Climatic, orographic and pedological characteristics of the studied localities were also taken into account. 相似文献
3.
我国某些常见化石硅藻的环境分析 总被引:6,自引:0,他引:6
蒋辉 《Acta Botanica Sinica》1987,(4)
本文详细研究了中国海表层沉积物中的常见化石硅藻,结果表明,这些种的分布范围及数量变化随环境的不同而变化。因此,根据柱状样品中这些种类数量的变化,能够推断古气候变化,恢复古地理环境,再现海平面波动历程,进而划分、对比第四系地层。 相似文献
4.
水洞沟遗址的环境与地层 总被引:11,自引:2,他引:9
水洞沟第四纪地层可与萨拉乌苏河组上段对比。水洞沟遗址包含有新石器和旧石器晚期文化,其旧石器晚期文化发生在距今20,000多年至10,000多年间的黄土状粉砂土中,即发生在末次冰期主冰期的干冷环境下,比发育在距今约35,000—50,000年间的萨拉乌苏河旧石器文化为晚。 相似文献
5.
Jeffrey D. Brawn 《Oecologia》1991,86(2):193-201
Summary Environmental conditions can influence the expression and correlations of phenotypic traits. I studied phenotypic plasticity in reproductive traits of Western Bluebirds breeding in northern Arizona. Data collected over 4 years on two contrasting habitats identified significant spatial and temporal variation in bluebird reproduction. Clutch size was similar over different environmental conditions whereas timing of clutch initiation, percent fledging success, and frequency of second nest attempts were flexible. Correlations between traits varied widely—often changing sign—among samples from different years or habitats. Correlations of traits with reproductive success were also dependent on environmental conditions. Variation in traits reflected behavioral responses by nesting adults to differences in time for breeding and feeding conditions. Density of trees differed between habitats and had opposing effects on these environmental variables; breeding seasons were generally longer, but feeding rates to nestlings were lower on the more open habitat. Late Spring snows delayed reproduction and increased the importance of limited time for breeding; feeding conditions were more influential following a dry Spring. This and other studies illustrate that data on phenotypic plasticity are important when evaluating the ecological and evolutionary forces underlying life histories. 相似文献
6.
Personnel records kept by military units of American colonials during the French and Indian War (1755-1763) are analyzed for relationships between environmental factors and stature. A robust American economy and direct access to high-quality food were apparently critical to tallness of this white American male sample. American-born men were taller at all ages than those who had migrated from Europe. January temperatures, rural versus urban birth, and ethnicity also showed stature relationships within the American-born group; thermal effects were by far the strongest of the non-nutritional factors. 相似文献
7.
8.
我国银杉自1955年发现以来,陆续发现了它的新分布,至今已知在四省、区7个分布区的30多个分布点上,自然生长着银杉3200余株。它们是:广西花坪林区(越城岭南部)6个点有银杉1040抹,其中高5米以上的68株,1~5米的49株,1米以下的923株,最高21.1米,最大胸径83厘米;广西大瑶山4个点有银杉143株,其中高10米以上的94株,1~3米的3株,1米以下的46株,最高30米,最大胸径79.2厘米;湖南罗汉洞(越城岭北部)2个点有银杉58株,5米以上的有45株,最高18米,最大胸径43厘米;湖南罗霄山脉八面山有银杉707株,高1米以上的334株,最高24米,最大胸径46厘米;四川南川金佛山(大娄山东段北部)6个点有银杉527株,其中成年树400余株,最高17米,最大胸径50厘米;百枝山有银杉52株,最高8米,最大胸径27厘米;贵州道真沙河林区(大娄山东段南部)3处12个点有银杉729株,其中高5米以上的105株,2~5米的209株,1~2米的111株,1米以下的304株,最高18.8米,最大胸径48厘米;贵州桐梓白菁有银杉10株,高4~5米的2株,1~3米的6株,1米以下的2株。 银杉分布区范围自北纬24°5′~29°13′14″,东经107°10′~113°40′。其垂直分布自海拔940~1840米,金佛山银杉分布最高,为1600~1840米;罗汉洞银杉分布最低,为940~1060米。分布区内,年均温8.2°~17℃,绝对最低温 相似文献
9.
K. P. Kollipara L. Singh T. Hymowitz 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1994,88(8):986-993
Variation in the trypsin inhibitors (TIs) and the chymotrypsin inhibitors (CIs) among 69 pigeonpea [Cajanus cajan (L.) Millsp.] strains from a wide geographical distribution and among 17 accessions representing seven wild Cajanus species was studied by electrophoretic banding pattern comparisons and by spectrophotometric activity assays. The TI and CI electrophoretic migration patterns among the pigeonpea strains were highly uniform but varied in the inhibitor band intensities. The migration patterns of the inhibitors in the wild Cajanus species were highly species specific. The mean TI activity of pigeonpea strains (2279 units) was significantly higher than that of the wild Cajanus species (1407 units). However, the mean CI activity in the pigeonpea strains (62 units) was much lower than that in the wild species (162 units). Kenya 2 and ICP 9151 were the lowest and the highest, respectively, in both the TI and CI activities among all the pigeonpea strains used in this study. A highly-significant positive correlation was observed between the TI and CI activities. The Bowman-Birk type inhibitors with both TI and CI activities were identified in all the pigeonpea strains and also in the accessions of all the wild species except C. volubilis (Blanco) Blanco. The C. volubilis accession ICPW 169 was found to be null for both CI bands and CI activity. Environment, strain, and environment x strain interaction showed highly-significant effects on both the TI and CI activities. Growing the pigeonpea strains at a different environment from their area of adaptation increased TI and CI activities and also altered the maturity period. 相似文献
10.
Summary Despite extensive discussions during the last 20 years stromatolites are still used by many geologists as unequivocal indicators
of very shallow-water conditions. We investigated four stratigraphic units from the Lower and Middle Jurassic of southern
Germany (Posidonien-Schiefer, Amaltheen-Ton) and of the Northern Calcareous Alps (Adneter Kalk, Klauskalk), which were formerly
interpreted as shallow marine sediments by some authors due to the occurrence of stromatolites. Our interpretations of the
macro-, micro- and ultrafacies of these sediments are not compatible with shallow-water settings. We therefore propose a deep-marine,
aphotic origin of these stromatolites.
Former interpretations of the Posidonien-Schiefer as a shallow-water deposit are mainly based on the occurrence of stromatolites.
We favour the model of a temporarily stagnant, deep, aphotic basin for these planktonrich sediments. Particles resembling
ooids, but lying within mudstones cannot be taken as evidence for shallow agitated water. They either formed within the mud
or are allochthonous.
The deep-water setting of the red limestone of the Alpine Early and Middle Jurassic is indicated by a lack of platform-typical
components like coated grains and phototrophic benthos and by shells of plankton and nekton forming a major part of the sediment.
Stromatolites occur on the steep slope of a drowned Rhaetian reef with an estimated relief of 50–100 m and immediately below
and within radiolarian limestones, deposited below the aragonite compensation depth (ACD).
The aphotic stromatolites show some morphological differences to their shallow water counterparts. In all of our sections
they occurred during intervals of reduced sedimentation. They form only thin horizons and probably grew very slowly. Mineralizations
by Fe−Mn oxides and phosphate are very common. The presence of a microbial film is evident from binding of sedimentary particles,
but the nature of the microbes is not known. Growth habits within the very distinct environments of red limestone and black
shales show some common features, but also clear differences.
The microproblematicumFrutexites
Maslov is a very common component in deep-water stromatolites, but may also itself form small crusts or dendrolites. It occurs in
two different forms. Opaque, slender forms with indistinct outlines probably grew within the weakly lithified sediment. Thicker,
transparent forms with well defined outlines are found in cavities and probably also grew on the seafloor. Well preserved
specimens display an internal fabric of radially arranged fibres of Fe−Mn oxides and calcite. It is suggested that calcite
or aragonite were one original mineralogy ofFrutexites, which was later replaced by Fe−Mn oxides or phosphate.
It is not certain whetherFrutexites is an organic, biomineralized structure or an inorganic mineralization, but the variable mineralogy and growth forms in different
environments point to an organic origin. But even if organic, the occurrence in cryptic habitats and negative phototactic
growth-directions make it clear thatFrutexites was not phototrophic. 相似文献