全文获取类型
收费全文 | 146篇 |
免费 | 10篇 |
出版年
2011年 | 2篇 |
2010年 | 2篇 |
2009年 | 2篇 |
2008年 | 6篇 |
2007年 | 2篇 |
2006年 | 3篇 |
2005年 | 4篇 |
2004年 | 3篇 |
2003年 | 2篇 |
2001年 | 2篇 |
1998年 | 2篇 |
1993年 | 1篇 |
1992年 | 1篇 |
1991年 | 1篇 |
1990年 | 3篇 |
1989年 | 1篇 |
1988年 | 2篇 |
1987年 | 2篇 |
1985年 | 2篇 |
1984年 | 3篇 |
1983年 | 1篇 |
1982年 | 3篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1978年 | 3篇 |
1977年 | 4篇 |
1976年 | 4篇 |
1975年 | 2篇 |
1974年 | 1篇 |
1973年 | 5篇 |
1972年 | 4篇 |
1971年 | 2篇 |
1970年 | 1篇 |
1969年 | 1篇 |
1968年 | 1篇 |
1964年 | 2篇 |
1959年 | 3篇 |
1958年 | 4篇 |
1957年 | 10篇 |
1956年 | 5篇 |
1955年 | 7篇 |
1954年 | 5篇 |
1953年 | 3篇 |
1952年 | 8篇 |
1951年 | 5篇 |
1950年 | 6篇 |
1949年 | 5篇 |
1948年 | 3篇 |
1947年 | 1篇 |
1946年 | 1篇 |
排序方式: 共有156条查询结果,搜索用时 31 毫秒
1.
With the use of anticoagulants to prevent recurrence of thrombosis it is now possible to open a major artery which has been occluded by a thrombus, remove the thickened lining with the clot and restore the continuity of the vessel. Free vein grafts have been used successfully to replace arterial segments in the extremities. Vein inlay grafts are preferred in dealing with aneurysms of the abdominal aorta. The aneurysmal wall can be used to support the venous segments. It has been possible to by-pass aneurysms of the abdominal aorta by anastomosing the splenic artery to the left iliac artery. The use of the left superficial femoral artery as a by-pass to supply blood to the right leg is described. 相似文献
2.
Carbonic anhydrase in molluscs 总被引:1,自引:0,他引:1
3.
The pericentriolar material in Chinese hamster ovary cells nucleates microtubule formation 总被引:48,自引:38,他引:10
下载免费PDF全文
![点击此处可从《The Journal of cell biology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
The structure and function of the centrosomes from Chinese hamster ovary (CHO) cells were investigated by electron microscopy of negatively stained wholemount preparations of cell lysates. Cells were trypsinized from culture dishes, lysed with Triton X-100, sedimented onto ionized, carbon-coated grids, and negatively stained with phosphotungstate. The centrosomes from both interphase and dividing cells consisted of pairs of centrioles, a fibrous pericentriolar material, and a group of virus-like particles which were characteristic of the CHO cells and which served as markers for the pericentriolar material. Interphase centrosomes anchored up to two dozen microtubules when cells were lysed under conditions which preserved native microtubules. When Colcemid-blocked mitotic cells, initially devoid of microtubules, were allowed to recover for 10 min, microtubules formed at the pericentriolar material, but not at the centrioles. When lysates of Colcemid-blocked cells were incubated in vitro with micotubule protein purified from porcine brain tissue, up to 250 microtubules assembled at the centrosomes, similar to the number of microtubules that would normally form at the centrosome during cell division. A few microtubules could also be assembled in vitro onto the ends of isolated centrioles from which the pericentriolar material had been removed, forming characteristic axoneme- like bundles. In addition, microtubules; were assembled onto fragments of densely staining, fibrous material which was tentatively identified as periocentriolar material by its association of CHO can initiate and anchor microtubules both in vivo and in vitro. 相似文献
4.
Distribution and analysis of cabbage root fly pupal populations 总被引:1,自引:0,他引:1
5.
6.
B. E. FREEMAN D. B. JAYASINGH 《Biological journal of the Linnean Society. Linnean Society of London》1975,7(3):231-241
Pachodynerus nasidens (Latr.) is an inquiline in the disused cells of Sceliphron assimile Dahlbom (Sphecidae) and Eumenes colona Saussure (Eumenidae) in Jamaica. Within the area of distribution of its hosts it is virtually absent where the essential resources of water and of leaf-mining, flower-feeding or leaf-rolling caterpillars on bushes are further than 80 m from the nesting site. Its use of host cells is reduced where mean annual precipitation is less than 1200 mm and where altitude is less than 100 m. In trap-nests it can be collected only in shaded and (less frequently) in partly-shaded localities. Of six other inquilines also found, only Trypoxylon texense Saussure (Sphecidae) was sufficiently numerous to be an important competitor for host cells but evidence shows its competition was unimportant to Pachodynerus nasidens. High percentage mortality resulting from Melittobia chalybti Ashmead (Eulophidae) on P. nasidens did not limit utilization of host cells. During drought, fecundity of P. nasidens dropped from 14.0 (± 2.9) to 7.0 (± 1.4) eggs per female and this may have brought about local extinction and hence low utilization of host cells. Drought reduced longevity and the rate of oviposition, but had no effect on the speed of provisioning. 相似文献
7.
PATRICIA W. FREEMAN 《Biological journal of the Linnean Society. Linnean Society of London》1992,45(2):97-115
Upper canines in microchiropteran bats show a variety of cross-sectional shapes. A consistent feature of all species studied here is that the tooth is edged and not simply round or oval. Prominent sharp edges are positioned in several directions but particularly antero-medially toward the incisors and posteriorly toward the premolars. These edges appear to direct the cracks made in food items to the incisors or to the premolars. A continuous cutting edge is apparent in the occlusal view of the palate running from tip of canine to the ectoloph of the molars. Size and shape analysis indicates that larger bats have slender, rather than stouter, canines for their height, a condition that may be attributable to the nature of the prey. Most bats take prey that have little hard substance imbedded within. The compromises in tooth shape may vary between that of a terrestrial predator with short, conical canines for processing endoskeletal prey to that of a small flying predator with long, slender, edged canines for capturing and processing exoskeletal prey. Unicuspid teeth and how they might function in food break-up have been overlooked to the literature; such a study could lead to an understanding of how more complex teeth function. 相似文献
8.
啤酒多倍体酵母菌原生质体已成功地与单倍体原生质体进行融合。经细胞壁再生后,稳定的融合重组体被分离出来。这些融合体的基因分析表明,融合体中含有双亲的基因型。孢子形成良好,且每个子囊中含有四个孢子,每个孢子确实是二倍体。这样原生质体融合就提供了一个对啤酒酿造酵母进行遗传分析的方法。但是如果没有一个方便的杂交技术,这个方法将是很困难的。 相似文献
9.
D. CARL FREEMAN MICHELLE L. BROWN MELISSA DOBSON YOLANDA JORDAN ANNE KIZY CHRIS MICALLEF LEANDRIA C. HANCOCK JOHN H. GRAHAM JOHN M. EMLEN 《Biological journal of the Linnean Society. Linnean Society of London》2003,78(1):27-41
Fluctuating asymmetry measures random deviations from bilateral symmetry, and thus estimates developmental instability, the loss of ability by an organism to regulate its development. There have been few rigorous tests of this proposition. Regulation of bilateral symmetry must involve either feedback between the sides or independent regulation toward a symmetric set point. Either kind of regulation should decrease asymmetry over time, but only right–left feedback produces compensatory growth across sides, seen as antipersistent growth following perturbation. Here, we describe the developmental trajectories of perturbed and unperturbed leaves of pumpkin, Cucurbita pepo L., grown at three densities. Covering one side of a leaf with aluminium foil for 24 h perturbed leaf growth. Reduced growth on the perturbed side caused leaves to become more asymmetrical than unperturbed controls. After the treatment the size-corrected asymmetry decreased over time. In addition, rescaled range analysis showed that asymmetry was antipersistent rather than random, i.e. fluctuation in one direction was likely to be followed by fluctuations in the opposite direction. Development involves right–left feedback. This feedback reduced size-corrected asymmetry over time most strongly in the lowest density treatment suggesting that developmental instability results from a lack of resilience rather than resistance. © 2003 The Linnean Society of London, Biological Journal of the Linnean Society , 2003, 78, 27–41. 相似文献
10.
BELINDA E. MEDLYN REMKO A. DUURSMA DEREK EAMUS DAVID S. ELLSWORTH I. COLIN PRENTICE CRAIG V. M. BARTON KRISTINE Y. CROUS PAOLO DE ANGELIS MICHAEL FREEMAN LISA WINGATE 《Global Change Biology》2011,17(6):2134-2144
Models of vegetation function are widely used to predict the effects of climate change on carbon, water and nutrient cycles of terrestrial ecosystems, and their feedbacks to climate. Stomatal conductance, the process that governs plant water use and carbon uptake, is fundamental to such models. In this paper, we reconcile two long‐standing theories of stomatal conductance. The empirical approach, which is most commonly used in vegetation models, is phenomenological, based on experimental observations of stomatal behaviour in response to environmental conditions. The optimal approach is based on the theoretical argument that stomata should act to minimize the amount of water used per unit carbon gained. We reconcile these two approaches by showing that the theory of optimal stomatal conductance can be used to derive a model of stomatal conductance that is closely analogous to the empirical models. Consequently, we obtain a unified stomatal model which has a similar form to existing empirical models, but which now provides a theoretical interpretation for model parameter values. The key model parameter, g1, is predicted to increase with growth temperature and with the marginal water cost of carbon gain. The new model is fitted to a range of datasets ranging from tropical to boreal trees. The parameter g1 is shown to vary with growth temperature, as predicted, and also with plant functional type. The model is shown to correctly capture responses of stomatal conductance to changing atmospheric CO2, and thus can be used to test for stomatal acclimation to elevated CO2. The reconciliation of the optimal and empirical approaches to modelling stomatal conductance is important for global change biology because it provides a simple theoretical framework for analyzing, and simulating, the coupling between carbon and water cycles under environmental change. 相似文献